June 1S91.] 



PSYCHE. 



97 



THE EMBRYOLOGY OF A COMMON FLY.* 



Since 18S6 five investigators, Kowalevsky, 

 Blochmann, Biitschli, 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 the 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 

 he 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, Biitschli 

 and Voeltzkow and to this conclusion Prof. 

 Graber assents. In this important point he 



*Verg'leichende 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. xSSip. (4to. p. 257-314. 10 

 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 blastopore 

 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 ectodermic 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 walls are con- 

 sequently 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 



