338 



IX 'SECT 'A. 



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 



A B appendages. In many Insects (cf. Hy- 



drophilus) a certain number of appen- 

 dages of the same nature as the an- 

 terior 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 ambulatory appendages. 



In Apis according to Biitschli (No. 

 405) all the abdominal segments are pro- 

 vided with appendages, which, always re- 

 main 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 11 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 

 011 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 abdominal segments 

 (tig. 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 nie 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 abdominal segments, 

 and this view is to some extent supported by more recent observations 

 (Kraepelin, etc.), and if it holds true for the Bee must be regarded as 

 correct for other cases also. 



As to the order of the appearance of the appendages observations are 

 as yet too scanty to form any complete scheme. In many cases all the 

 appendages appear approximately at the same moment, e.g. Hydrophilus, 

 but whether this holds good for all Coleoptera is by no means certain. 

 In Apis the appendages are stated by Biitschli to arise simultaneously, 

 but according to Kowalevsky the two mouth appendages first appear, 

 then the antenna?, and still later the thoracic appendages. In the Diptera 

 the mouth appendages are first formed, and either simultaneously with these, 

 or slightly later, the antenna?. In the Hemiptera and Libellulidse the 



FIG. 187. Two STAGES IN THE 



DEVELOPMENT OF HYDROPHILUS PI- 



CETJS. (From Gegenbaur, after 

 Kowalevsky.) 



Is. labrum; at. antenna; md. 

 mandible; m.r. maxilla I.; //.max- 

 illa II.; p' p"p"'. feet; a. anus. 



