July iSyi.] 



PSYCHE. 



115 



legs of the caterpillar-like larva. He finds 

 that during embryonic life each of the eleven 

 abdomidal segments presents a pair of appen- 

 dages. Those on the ist and 7th-c)th segments 

 soon disappear, while those on the remaining 

 segments persist as the prolegs of the larva. 

 The pair of appendages on the tenth segment, 

 which are at the time of their origin in 

 line (homostichous) with the appendages of 

 the preceding segments, move pleurad, and 

 thus become ectostichous. On the nth seg- 

 ment the appendages ("afterspitzchen") are 

 close together (entostichous). It is this last 

 pair of appendages which corresponds to the 

 anal legs of Lepidoptera, since, in the true 

 caterpillars, according to Prof. Graber, the 

 anal legs do not belong, as Haase and other 

 investigators aver, to the tenth, but to the 

 eleventh abdominal segment. Prof. Graber's 

 figures are certainly far from being conclu- 

 sive on this point. The peculiar cerci of 

 Lyda belong to the tenth segment and are 

 not therefore homologous with the anal legs 

 of Lepidopterous larvae. 



It is also interesting to note that the forma- 

 tion of the embryonic envelopes and the 

 manner in which the dorsal body-wall is com- 

 pleted in the embryo Hylotoma strikingly 

 resemble what is observed in Lepidoptera. 

 This fact may prove to be of use as further 

 evidence of a common ancestry for the Lepi- 

 doptera and Hymenoptera. The embryology 

 of Hylotoma certainly appears to bear out the 

 conclusion long since drawn from the adult 

 structure of the Phytophaga, viz. : that this 

 group is the most primitive among existing 

 Hymenoptera. When we pass from a Tenth- 

 redinid to an Apid it appears that the embry- 

 onic envelopes show a tendency to become 

 aborted, just as they do in the Diptera, in 

 passing from an old form like Chironomus to 

 a recent form like Musca. The general valid- 

 ity of this remark is in no wise impaired by 

 the difference in the kindsjof abortive change 

 undergone by the envelopes in the two orders. 

 W. M. Wheeler. 



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BLOW-FLY. 



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