Article beginning on page 89.
Psyche 11:89-101, 1904.

Full text (searchable PDF)
Durable link: http://psyche.entclub.org/11/11-089.html

The following unprocessed text is extracted from the PDF file, and is likely to be both incomplete and full of errors. Please consult the PDF file for the complete article.

tubscribers in the
;o ; $1.25 to those
at$s.oo a voIume.
Remittance should
ion.
additional copies
FOH, MASS.
mrn of the Boston
third Tuesday of
a. Entomologists
ad in the order la which
to make room for new
mom. Theat ahould be
olledon, from all pim
ila BaaSarckvt, includim
fcimem ahowins unusual
ti* Zoology. W, L. W.
PSYCHE.
THE DEVELOPMENT OF THE ROSTRUM IN RHYNCOPHOROUS COLEOPTERA.- PLATES VI-IX. ,
BY ETHEL M- MCCLENAKAN, LAKE FOREST, ILL. I. Introductory.
MUCH has been learned of late from the study of the development of parts which suddenly appear externally in insects at transformation. There remain a
few such parts which have not as yet .received the attention of investigators. One
of these is the rostrum of rhyncophorous Coieoptera, Notwithstanding its size and
singular appearance, and the interest bestowed upon it as an adult structure by systematists, I cannot discover that its development has received any attention whatever. Although it is long, often longer than legs or wings, and although appendage-like in appearance, it is not an appendage in the same sense as these, but is a prolongation of the front part of the head and carries the antennae upon its sides and the mouth parts at its rip. Dr. Le Conte, in the preface to his synopsis of the Rliyncophora of North Amer- ica, in enumerating important questions for further study in the groups, said, "The homoiogies of the parts of the head, by reason of which the front portion becomes extended into a beak, and the basal piece on the under surface (which separates the gular sutures in normal Coleoptera) disappears, are also worthy of attention/' This study of the developmerit of the rostrum lias been undertaken because it '
seemed likely to yield answers to some of these questions of the systematist, and at the same time to throw some new light on the general problems of meta- morphosis. -
I have used, main iy, the two species of Rhynco phora, Mo~my/ktts v$betu/~ts Fabr. and Baiadnm nasicxs Say, The former lives its whole developmental life in the. capsules of the blue flag - a period of about nine week1 JSdaninus nasi- cus (Plate VI, fig. I) is known as the acorn weevil. The adult bores a hole into the developing acorn and in it lays her egg. This takes place in the summer or early fall.
It soon hatches into a small white larva and grows rapidly, living upon the



================================================================================

90 PSYCHE [October
meat of the nut which, as a rule, it will have wholly consumed by the time it is grown (Plate VI, fig. 2). When the nut falls the larva leaves it, buries itself in the earth at considerable depth, which is probably to avoid freezing. Ordinarily but one larva lives in a nut, though two and even three are sometimes found. Since in this case they are invariably smaller there is an evident lack of nourishment. - The adults appear above ground any time after the first, of June, some even as late as July or August.
.
My material, which abundantly represented all stages of rnetiirnorphosis, was obtained by collecting a large quantity of acorns of the white oak {Quercas tz&) when they fell in autumn, and placing them on a box filled with earth and grass sod. In a very little while the larvae bored out, entered the earth and buried chew selves near the bottom of the box. This was kept in the Laboratory where the normal temperature was about 2 1' C. and probably never lower than 18' C. Specimens were taken out at weekly intervals and fixed. Through the winter there were no signs of metamorphosis.
This suddenly took place in the spring.
The first imago was seen April 9th, and within the next two weeks they were abundantly found.
April 23 the remaining specimens which represented ail stages aE development were taken out and fixed. This does not agree with Miss Murt-
feldt's results, but if left undisturbed they might possibly not have emerged until much later?
Salam~us naskus Say (Plate VI, fig. x), representing the extreme development of the Rhyncophorous rostrum, and, being the species I had under observation and control, has been the chief subject of study for the following paper. The account of the larva in particular is drawn wholly from Balanhus wbile Monutychus has served best for the study of internal metamorphic processes. Methods- For fixation 70 % alcohol, first heated' to boiling, was used with , excellent results; paracarmine was used for staining in toto with a counterstain of orange or methyl blue on the slide ; haematoxylin was mainly used for staining sections followed by eosin or picro-fuchsin as counterstain; whole preparations were stained with boraxxarmine and differentiated with acidulated alcohol The development of me rostrum will be best understood by studying the parts concerned, firstly, in the larva, which has no rostrum ; secondly, in the adult, which has it complete; and thirdly in transforming larvae and pupae, which show every phase of its growth.




================================================================================

[October
by the time it is
lurks itself in the
. Ordinarily but
1es found. Since
nourishment.
June, some even
itamorphosis, was
lit (Quercus alba}
i earth and grass
and buried them-
Hratory where the
ian &C.
\rough the winter
ce in the spring.
weeks they were
sented all stages
with Miss Murb
.ve emerged until
erne development
- observation and
ir. The account
Momnychus has
;, was used with
h a counterstah
used for staining
ole preparations
alcohol.
udying the parts
the adult, which
hich show every
It. The Larva.
The larvae of Salaniaus nasiws Say vary- considerably in size. The average
lam, however, is about 1 j& mm. from tip to tip; measured over the back, as it lies in its ordinary curled position, about 18 nun, ; and 4 mm. in diameter. It is
uniform1y white in color with brown mandibles and an impertect dorsal protl~oracic shield of yellowish chitin. On each side are four rows of very small setae, two on either side of the spiracles. The ventral setae arise from conspicuous prominences. A few scattering ones lie on the under side of die body. This larva (Plate VI, fig. 2) is of a very degenerate type. It has no organs
except those for feeding.
It wholly lacks eyes, antennae and legs. Correlated
with the absence of eyes, the brain is destitute of optic iobes. The
ally small and the short, and close-set face and mouth parts give remarkable extension they will undergo at traosfomiation. MOm PARTS.
Save for a slight reduction in maxillae and labium the mouth parts are much like those of other beetle larvae. The labrum is broadly rounded and supports near its edge ten spines and on the dorsal surface two or three pairs additional. At die middle of its posterior edge it is slightly produced backward into the ciypeus. The mandibles (Plate VIII, fig. 12 md) are somewhat triangular in outline with an ill-defined tooth upon the inner edge and two larger ones at the tip. They are moved by two large muscles (Plate VIII, fig. s 2 ab. m.1 and ad. m.3) which occupy the greater part of the head. The adductor is (ad m.3) larger and is attached through a stout tendon to the inner basal angle of the mandible. It is made up of numerous straight fibres, some of which arise from the wait of the head, others from a median dorsal chitinous endoskeletal ridge. The fibers of the abductor (ah. d.) are all attached to the latero-ventral wall of the epicraniuni. These unite into a short tendon which connects with the outer basal angle of the mandible. Maxillae (Plate VIII, fig. 12, mx.) are comparatively simple. Cardo and stipes meet at a right angle. The latter is fused with the Iacinia, which is armed on its edge with a row of ten spines. The gales is two jointed with four minute prominences on its tip.
Paipus is wanting. Three sets of muscles serve to move tfie maxilla- two adductor and one abductor. The larger adductor (Plate VJIJ,
fig. 12, arf. ml) is inserted near the tip of the laciriia. It is a compact band of
fibers and takes its origin at the rear of the head. The lesser adductor (Plate VIII, fig. 12, ad, m.') springs from the ventral part of the tentorium and is inserted



================================================================================

92
PSYCHS [October
near the middle of the stipes.
The abductor (Plate VIII, fig. 12, ad. m?) springs with the latter from the tentorium and is inserted on the external angle of the stipes beyond the basal hinge* Four large spines arise from the external face of the maxilla ; one near the union of cardo and stipes ; two near the base of the galea and one upon the basal segment of the galea. The Zatium (Plate VIII, fig. I z, 2.) is considerably reduced and its parts con- solidated. The mentum is large. Paraglossae are broad ; the glossa is triangular: the palpi are short and two jointed. Two pairs of muscles (Plate VIII, fig, 13, l. m.} take origin in the posterior region of the head and are inserted into the tip of the labium.
Thus there appear among the muscles that move the mouth parts two pairs springing from the tentoriutn and belonging to the maxillae ; and five pairs spring- ing from the hinder parts of the walls of the head : =
Two large pairs belonging to> the mandibles. I
One lesser pair belonging to the maxillae. !
Two still smaller pairs belonging to the labium. I
J
The relations of these muscles will be found of importance when the shifting of parts in development is considered.
I
ANTERIOR PARTS OF ALIMENTARY CANAL AND SALIVARY GLAKDS. I
!
i
i
The Alimentary Canal agrees in general with that of other phytophagous beetle larvae.
The esophagus is short, merging into the proventriculus at the end ofthe prothoracic segment.
Numerous dilator musclesarranged along the esopha- gus are attached to the dorsal wall of the head immediately back of the labrum. -
Thepr07~t"ntnå£d1 or crop is large and cylindrical in shape, slightly tapering at its posterior end into the long and twisted ventricdus, along each side of which isarranged in a longitudinal series a row of somewhat conic caeca, whose individ- ual length is somewhat less than the diameter of the ventriculus, "i
The Salivary Glands consist of a single pair of long, tortuous, simple tubes lying at the sides of the esophagus.
The tubes are slender, showing about two and a half cells in cross section, the individual cells rounded externally, giving an irregular outer surface to the gland, and internally the cavity winds a tortuous course between the internal prominences of the cells. The nuclei are more or less hemispherical, often more or less concave on the inner face and they always ' extend on that face numerous conic or jagged processes toward the lumen of the



================================================================================

[October
, at. m.9 springs
ngle of the stipes
:mat face of the
iase of the galea
nd its parts con-
ssa is triangular :
TII, f '-. 12, I. w.)
ttto the tip of the
b parts two pairs
five pairs spring-
when the shitting
ler phytophagous
riculus at the end
along the esopha-
of the labrum.
, slightly tapering
!a& side of which
xa, whose individ-
nous, simple tubes
howing about two
:ternally, giving an
winds a tortuous
ei are more or less
i and they always
d the lumen of the
' III. Imago.
The most striking peculiarity of the adult beetle, a characteristic of all Rhyn- cophorous Coleoptera, is a prolongation of the anterior part of the head which forms the rostrum.
It is with this part that we are chiefly concerned. An under-
standing of its development will be best had if its structure in the adult beetle is first clearly understood and compared with that of the larva, just described. The rostrum of Rliyncophora is uniquein that it is not made up oi elongated mouth parts' as in Hymenoptera, Hernipera, Diptera and Lepidoptera; not even in part, as in scorpion flies (Mecoptera) ; but it is the greatly elongated fore part of the head, the part between the eyes and the mouth ; and it bears the mouth parts, which are similar in shape to those of other Coleoptera, at its apex. It varies from 33 to 7 mm. in length in BaZa?~i~~us?~astciii, being generally longer than -
the entire body of the weevil* It is gently decurved and has a deep groove on each side for the reception of the reflexed scape of the antenna. In it the
usual sutures between the head sclerites are entirely obliterated by fusion and the scanty external evidence as to its composition is derived from the position of eyes. antennae and the mouth parts.
This alone indicates that it is composed of fused frons, genae and gula of the normal insect head - a view which ontogeny substan- tiates, as we shall see under a subsequent heading. MOUTH PARTS.
In these two weevils at least the mouth parts, generally speaking, show rather close correspondence with those of the larvae. They are more elongate and have sharper cutting edges.
Each mandible bears also at its base a singular process as long as (Plate IX, fig. 18) or longer than (Plate IX, fig, 15) the body of the mandible. This process
projects posteriorly down the pharynx to the entrance of the esophagus. It is
thickly beset with posteriorly directed prickles similar to those of the surrounding pharyngeal wall.
This process doubtless serves for the propulsion of the food down the narrow passage-way of the anterior end of the alimentary canal. With the swinging of the mandibles upon their hinges the two pharyngeal processes appended to their inner basal angles, lying side by side in the pharynx are drawn forward and pushed back- ward. Such is the direction of the prickles that the backward movement carries the food along.
After discovering these pharyngeal processes, I searched for some account of



================================================================================

PSYCHE [October
them in such entomological literature as was accessible. The mouth parts of the Coleopiera having been so much used in classification I could scarcely believe that these were iindescribed. yet I have not discovered any mention of them. - Mailhe have the same parts as in the larva, though more highly differentiated. edge of tile tacinia is covered with a dense fringe of hairs. The plea is four jointed and the palpus is wanting.
The labium (Plate IX, fig. 19) is quite different in its shape from that of typ ical Coleoptera. The sub-menturn is long and broader at the middle than at the ends. The menturn is of about the same length but more slender.. The para- glossa is short and widens at the anterior end beyond which a long narrow glossa projects.
Both are tipped with numerous small spines. The palpi are small and
e Hjå´po@aryn is well developed, at least in Mot~onychus (plate IX, fig. , with a free tip and covered with recurved prickles, he muscles which move mouth parts lie in the more convex part of the head ry much the same positions as in the larva. The tendons which are there
er short or altogether wanting, have developed with the rostrum. They lie
'
e ventral side and connect the muscles in the head proper with the append- the apex. (Plate IX, fig. 14, /.)
e antennae are situated upon the beak from one to two mm. from the more part of the head.
The scape is very long.
The slender pedicel has seven
gments.
The ovate club consists of three or four, more or less, consolidated Two sets of muscles move each antenna.
Their fibers originate in the ten-
torium and shortly unite into four uniformly thread-like tendons which are inserted upon the round basal piece of the scape ; two, probably used for making the for- ward movements, upon the inner side ; and two, which make the opposite back- ward movements, upon the outer side (Plate IX, fig. 14, am. and aÌöf.) THE SHIPTIKG OF MOUTH PARTS IN BALANISUS. he relative positions of mouth parts differ considerably in these two species. wnych~ts the order is that of normal Coleoptera. During the metamorphosis Balanintts, however, a curious shifting in positions of mandibles and maxillae es place. The exterior sides of the mandibles turn ventrally, approximating the ormal positions oE maxillae. The maxillae, in turn, are pushed dorsally between andible and mouth, the brush-like edges of their laciniae protruding between man- ible and labrum. The mandibles then move vertically as described by Dr. Horn Amer. Philos. Soc. Trans., p. W, 18731, who conceived them as working upon of shears.




================================================================================

nouth parts of the
arcely believe that
if them. -
ghly differentiated.
The galea is four
: from >hat of typ-
aiddle than at the
ender~ The para-
long narrow glossa
dpi are small and
ius (Plate IX, fig.
; part of the head
is which are there
ostrum. They lie
r with the append-
nm. from the more
pedicel has seven
less, consolidated
ginate in the ten-
which are inserted
>r making the for-
the opposite back-
1 ad).
JS.
.
these two species.
he metamorphosis
bles and maxillae
approximating the
d dorsally between
ding between man-
ibed by Dr. Horn
I as working upon
These have considerably altered the proportions they have in the larva. The
salivary glandi are not :he same, but a new development ; new armature has been differentiated in the walk- of the proventriculus, and new tracheal branches have penetrated tin; rostrum.
The pharynx passes over into the esophagus (Plate IX, fig. 14, 08) which extends as a -.lender tube back into the prothorax and there abruptly widens into a barrel shagx; proventriculus (pv) . This in Mmmych~ir is lined with eight double rows of tra~sversely placed sharp edged plates of chitin; each row containing about sixty plates. The ventral wail of the pharynx (Plate IX, fig, 17) is made of thick chitin and is incapable of contracting or expanding. That is the function --
of the dorsal wall which is lined with but a thin coat and covered with prickles. The short elrvator muscles (Plate IX, fig. 14 M, and figs. 16 and 17) are attached in two longitudinal rows to this wall and aid in swallowing by drawing out the folds of the dorsal wall and enlarging the cavity. Around this side are several rows of semicircular muscle bands which contract it again into its position of rest. The esophagus is who11 y surrounded by circular muscles. Close betide the .mandibular abductor tendons lie a pair of simple tubular salivary glantls which extend directly through the rostrum to the dorsal part of prothorax where their ends are twisted with many convolutions (Plate IX, fig. 14; $.&.).
A single pair of tracheae distribute their branches through the beak. IV. Metamorphosis. t
~ ~ E R N A L FEATURES OF THE METAMORPHOSIS OF THE HEAD. A compaiison of larva and imago shows great changes in both internal and external anat~uny.
The larva merely exists to eat and grow and accumulate fat for its metamorpSiosis.
It lives a sequestered, inactive life and only the organs neces- sary for such
life are developed.
The adult, on the contrary, lives the active life of ordinary "beetles.
It possesses wings, legs, eyes and antennae in addition to the larval structures.
The transformation from the degenerate larva to the highly organized adult beetle, whether it occurs immediately at the end of growth, as in Afono?~vdtd~, or after a long period of quiescence with suspension of all vital activity, as in MU- ninus, when \\ does begin takes place rapidly.



================================================================================

PSYCHS [October
As a preliminary, certain of the old larval structures are gradually broken own.
The fat in the anterior end of the body disintegrates and is made ready to e used in building up the new structures of the imago. As the old muscles of the head disintegrate the whole anterior end shrinks begins to take shape.
If the chitin be
nditlon shown in Plate VI, figs. 3, 4 and 5. begun to form but are still very crudely shaped ; the rostrum is already apparent, though broad and short and with walls transversely corrugated.
The antennae also are forced into many folds by reason of their rapid increase in length. The folds suggest the segmentation of the adult antenna. Real
take place until the pupal stage.
rostrum immediately back of the labrurn
nna.
This in the adult is the longer part of
The mouth parts of the old larva are thick, broad and shapeless, yet resemble in general outline homologous parts in the adult. The labrum is short and slightly
bitobed. In the very old larva the large mandibles, always very prominent, are ' somewhat, though not deeply, serrated on their inner edges and otherwise quite similar in form to the stout biting jaws of the adult. Ventral views of the develop- ing rostrum (figs. 4 and 5) show the bibbed maxillae and trilobed labium. The labial glossa and paraglossae at this stage are large and distinct. In Mownychs (fig. 4) the hypopharynx protrudes beyond the labrum. A faint differentiation of tissue upon each side of the epicraniurn shows the outline of the large compound eye. Near the center of this is a small opaque spot where the optic lobe of the brain is developing. THE DEVELOPMENT OF THE BEAK.
aracteristics the hypodermic is the same for at1 the parts of beginning of metamorphosis it is very thick. The cells are closely crowded together and elongate.
The
fully one-third of the cell. They are filled and increase in size of the parts the hypoder- reed into folds.
In this way the entire beak and antennae are crowded their final length, and the pupal stage is entered



================================================================================