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Psyche 6:97-98, 1891.

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June 1891.1
PSYCHE.
THE EMBRYOLOGY OF A COMMON FLY.*
Since 1886 five investigators, Kowalevsky, Blochmann, Butschli, Henking, and Voeltz- kow have contributed important observations on portions of the embryology of common
muscids (Calliphora, Lucilia>. To this list Prof. Graber's work is now to be added as the most comprehensive and voluminous. This
paper is worthy of special attention, coming as it does from an eminent entomologist who has for years been actively productive in a field which many a younger investigator has deserted after contributing a short memoir on some common insect.
Prof. Graber's treatise covers nearly the whole ground of embryonic development in Musca beginning with the cleavage of the egg and concluding with a description of th6 ner: vous system and the formation of the imaginal discs. To our knowledge of the preblasto- dermic stages he cannot be said to have ad- ded any really important facts, although he has succeeded in correcting some of Voeltz- kow's errors.
The formation and evolution of the germ- layers of Musca constitutes the all-important topic of the paper.
After devoting a pre-
liminary chapter to some observations on Aphis, in order to disprove Will's statement that the mid-gut arises from the yolk-cells (vitellophags), Prof. Graber attacks the sub- ject in Lucilia and Calliphora, pointing out step by step as he proceeds the points wherein fie agrees or disagrees with his predecessors. The main question : Do the vitellophags take part in the formation of the mid-gut? was answered negatively by Kowalevsky, Butschli and Voeltzkow and to this conc~~sion Prof. Graber assents. In this important point he *Vergleichende studien iiber die embryologie der insecten und insbesondere der musciden. Von Veit Graber. Denkschr. d. math. naturw. classe d. k. akad. d. wiss. Wien, bd. 56. IS$. (+to. p. 257-314. to plates.)
cannot be said to have made any great ad- vance, his observations being merely corrob- orative of the results obtained by other recent investigators besides those who have worked on Musca. The fatiguing length to which
Prof. Graber goes in describing his sections would be unpardonable, were it not that he had not read Heider's work on Hydrophilus or his present critic's paper on Doryphora before publishing.
To the important subject of the relations of the fore- and hind-gut to the blabtopore Prof. Graber has contributed some interest- ing observations, although his remarks, as we hope to show presently, must be received with some reservations. His results are very
briefly these : The fore-gut (stomodaeum) is formed near the anterior end of the gastrula raphe as a distinctly ectodertnic invagination whereas, on the other hand, the hind-gut (proctodaeum) appears to be formed as a
deepening of the gastrular groove at the pos- terior end of the embryo. Its walli are con- feequently of mesentodermic origin. Be-
sides the elongate median gastrula, familiar to all students of insect embryology, Prof. Graber describes two- pairs of grooves which run parallel with the median groove and also contribute in the formation of the mesento- dermic layer. These grooves thus constitute a lateral gastrulation. Their relations to one another and to the median groove are not eas- ily understood from the description and Prof. Graber should have introduced diagrams to show their exact position and extent. The true morphological significance of the lateral gastrulation is not explained and as nothing comparable to it has been observed in other insects, the observation has as yet only the value of an interesting and isolated fact. The author's suggestion that the small
grooves may be a new formation introduced for the purpose of augmenting the mesento- derm is, to say the least, improbable, when



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98 PSYCHE. [June ]@I+
we take into consideration the great extent Graber's work is chiefly valuable as showing of the median invagination in Musca ;and the to what an extent the embryonic develop- small size of the blastopore in certain Or- ment of a calyptrate muscid has been de- thoptera where no lateral gastrulation has flected from the ancestral path - in other been observed.
words, it is an admirable picture of one of One may venture to object to some of the the "short-cuts" in insect development. new terms of which Prof. Graber has been It will be remembered that the egg of the rather prodigal in his latest papers. The fly hurries through its whole development time-honored term ~btaetoderm" is easily in about 24 hours, that it is provided with a understood and it is difficult to see why it relatively small quantity of yolk, and that should be relegated to the biological attic for the characters of the secondarily developed effete nomenclature to make room for an only and degraded maggot have been reflected remotely suggestive term like "cycloblast." back into embryonic life. That this reflection Prof. Graber now dubs the yolk-cells "cen- has materially altered the original ontogeny trobla~ts" notwithstanding the termination as displayed by older forms such as the Or- 6blast" is properly applied only to tissues of thoptera and Hemiptera, is evident from the a germinal or formative character and not to fact that the embryo no longer exhibits the elements which, like the yolk-cells, degener- typical cephalic and thoracic appendages, to. ate and take no part in building up the insect. say nothing of the abdominal appendages It would be wiser to suspend the use of terms (embryos of bees, beetles with apod larvae like tbptychoblast" till we possess a better and fleas still develop thoracic legs!). More- knowledge of arthropod" germ-layers, as we over the ammion and serosa are rudimen- have still a great deal to learn on this sub- tary in Musca; the head has become pro- ject. In the meantime '4rnesentoderm'a is foundly and strangely modified and the quite clear and will answer all purposes. rnesodermic layer no linger exhibits thetypi- "Ent~myoderm" and "ectomyoderm" are cai paired coelomic cavities. It is, therefore, scarcely to be regarded as improvements on obvious that conclusions drawn from the theold terms, '~splanchnopieure"and"eoma- embryogeny of a muscid cannot without topteure." We supposed that Prof. Grater's extreme caution be extended to cover other terminological fecundity was exhausted ineects. It is further evident that to aecer- when he gave us the sesquipedalian, "ec- tain the exact path of development in an toptygmatorhegmagenoua ptychonotogony.'' insect that develops so rapidly a very great But these are small blemishes in a work number of eggs mast btf examined to insure which will rank among the more important certainty in regard to the different steps in contributions to insect embryology. the hurried sequence of tissue-changes. The chief vaiue of Prof. Graber's paper
Granting the correctness of Prof. Grabefs cannot be said to lie in a furthering of what observation that the proctodaeum is of mea. we must regard as oneof the chief aims of the entodermic origin, we may perhaps account study of insect development, viz: a know edge of the mutual phylogenetic relations of the existing orders of insects (often separated by wide gaps, towards the bridging of which comparative anatomy and paleontology have contributed only a little), and a knowledge of the relations of insects, as a class, to other arthropod groups and to their remote anca. tors, the annelids. In our estimation Prof. for this condition on 'the supposition that whereas in other insects of slow development the hind gut is not formed till after the clog- use of the posterior end of the blastopore, in Musca the processes of growth succeed one another so rapidly that the blastopore does not have time to close before the hind- gut is found. Thus the apparently mesento- dermic character of the hind gut would




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June 1891.1
PSYCHE.
be a secondary condition due to acceleration .of development.
The 10 plates with 127 figures illustrating Prof. Graber's papers are beautifully executed and are by far the most accurate ever pub- lished on the subject. It is to be regretted that Prof. Graber did not introduce larger, clearer and more numerous diagrams. The
need of these is especially urgent as it is next to impossible to obtain good surface views of the fly's egg, and mental reconstruction, even from such excellent sections as those given in the plates, is no easy task for the reader.
It is to be hoped that the next investigator who undertakes the study of the Musca egg will make use of the wax reconstruction
methods now so succesfully employed by
workers in other fields of embryology.
W. M. WHEELER.
OENEIS AND ITS EARLY STAGES.
At the last (May) meeting of the Cam-
'bridge entomological club Mr. S. H. Scudder spoke of the group of Oeneides as one of the most interesting of butterfly genera, partly because (using the word in a restricted sense) there was no other genus of butterflies in which so many species were common to the Old and New Worlds, but more because it is the only genus entirely restricted to high latitudes and altitudes and widely'spread in the world. Eight species occurred in Eu- rope-Asia, of which two or three were also found in North America, which possessed
besides at least eight or nine species.
One
would suppose that it would be one of the last with the early stages of whose life we should be acquainted, and this was the case until recently, but now more or less has been published
concerning eight of the species,
mostly from observations in this country, and it is understood that Mr. W. H. Edwards, to whom most of this advance is due, has full 01- tolerably complete histories of two or three more.
I had the good fortune, he remarked, to be the first to publish an
account of the early
stages of one of the species of the genus - Oeneis semidea, the only one found in New England,- due to the joint efforts of the late Messrs. Shurtleff and Sanborn and myself, though no one has yet carried the creature through from the egg. Since then most of the additions to our knowledge of American species have come from Edwards, but Fyles has published the history of Oe. jutta to which Fletcher and I have added something, and in Europe, where the same species oc- curs, Holmgren and Berg. One of the latest known species, Oe.macounii, is now almost completely known, thanks to Mr. J. Fletcher, who has published an account of it, and the egg and first larval stage have also been de- scribed by Mr. W. Beutenmuller. All that is known of chryxus, iduna, and ivalda, is due entirely to the indefatigable efforts of Mr. Edwards.
Of the European species also, it so chanced that I was the first to publish anything (a year previous to Berg's account of 0e.jutta) describing the egg and first larval stage of Oe.aello, the alpine species, to which nothing has since been added; and excepting Oe.
juttcz, before referred to, the early stages of only one other species, Oe. bore, are known, due to the studies of Sandberg.
Out of sixteen or seventeen species, then, recognized in the northern hemisphere, we now know more or less of the transforma- tions of about half the species not to mention the two or three which Edwards has worked out but not yet published. This is a remark- able showing for a group of butterflies with such a distribution, and brings out several features which are a little puzzling. First, there are two types of surface sculpture in the eggs; the more common is that in




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