408 



INSECTA. 



The antennae themselves can hardly be considered to have 

 the same morphological value as the succeeding appendages. 

 They are rather equivalent to paired processes of the prae-oral 

 lobes of the Chaetopoda. 



From the first three post-oral segments there grow out the 

 mandibles and two pairs of maxillae, and from the three following 

 segments the three pairs of thoracic appendages. In many 

 Insects (cf. Hydrophilus) a certain number of appendages of the 

 same nature as the anterior ones are visible in the embryo on 

 the abdominal segments, a fact which shews that Insects are 

 descended from ancestors with more than three pairs of ambu- 

 latory appendages. 



In Apis according to Biitschli (No. 405) all the abdominal segments are 

 provided with appendages, which always 

 remain in a very rudimentary condition. 

 All trace of them as well as of the thoracic 

 appendages is lost by the time the embryo 

 is hatched. In the phytophagous Hy- 

 menoptera the larva is provided with 

 9 n pairs of legs. 



In the embryo of Lepidoptera there 

 would appear from Kowalevsky's figures 

 to be rudiments of ten pairs of post-tho- 

 racic appendages. In the caterpillar of 

 this group there are at the maximum five 

 pairs of such rudimentary feet, viz. a pair 

 on the 3rd, 4th, 5th, and 6th, and on the 

 last abdominal segment. The embryos 

 of Hydrophilus (fig. 187), Mantis, etc. are 

 also provided with additional appendages. 

 In various Thysanura small prominences 

 are present on more or fewer of the abdo- 

 minal segments (fig. 192), which may 

 probably be regarded as rudimentary 

 feet. 



Whether all or any of the appendages 

 of various kinds connected with the 

 hindermost segments belong to the same 

 category as the legs is very doubtful. Their usual absence in the embryo or 

 in any case their late appearance appears to me against so regarding them ; 

 but Biitschli is of opinion that in the Bee the parts of the sting are related 

 genetically to the appendages of the penultimate and antepenultimate abdo- 

 minal segments, and this view is to some extent supported by more recent 



FlG. 187. TWO STAGES IN THE 

 DEVELOPMENT OF HYDROPHILUS 



PICEUS. (From Gegenbaur, after 

 Kowalevsky. ) 



Is. labrum; at. antenna; md. 

 mandible; mx. maxilla I.; //. max- 

 illa II.; //"/". feet; a. anus. 



