THE DEVELOPMENT OF AXTS. 



nutus quadriceps feed directly on the pith of the plants in which the 

 insects nest (see Fig. 168). 



The internal structure of the larva, which is essentially that of the 

 mature embryo, has been described by Ganin (1876), Dewitz (1877, 

 1878), Xassonow (1886) and Karawaiew (1898, 1900) for Formica, 

 M \nnica and Lasius, by Berlese (1901) for Tapinoina, and by Perez 

 ( 1902 ) for Formica rufa. In the following account I have followed 

 Perez. The alimentary tract of the larva ( Fig. 44 ) is much simpler than 

 that of the adult described in Chapter III. The thin outer integument 

 is folded into the body to form the walls of a slender pharynx and 

 oesophagus, which is, therefore, of ectodermal origin and corresponds 

 to the stomodseum of the embryo. Muscles extend from the walls of 

 the pharynx to the dorsal integument and function as dilators during 

 the sucking or imbibing movements of 

 the larva. At its posterior end the 

 pharynx opens on an elevated, valvu- 

 lar papilla into the chylific stomach, 

 which is equivalent to the embryonic 

 mesenteron, or mid-gut. It is a spa- 

 cious, ovoid receptacle, somewhat at- 

 tenuated anteriorly in the future 

 proventricular region and closed pos- 

 teriorly where it unites with the an- 

 terior end of the hind-gut, or embry- 

 onic proctodseum. The latter is 

 formed by a tubular invagination of 



the ectoderm similar to that which 



FIG. 41. Larva of Ponera 



forms the OeSOphagUS. Owing to the pennsylvanica. (Original.) a, Larva 



closure between the chylific stomach 

 and the hind-gut, all the undigested 

 portions of the larval food enclosed in 



the series of successively sloughed peritrophic membranes, accumulate 

 in the cavity of the stomach and form a black, elliptical mass, the me- 

 coninm, which often shows through the translucent body walls of the 

 larva. The hind-gut, is differentiated into two regions, a more slender, 

 tubular anterior portion, the small intestine, and a more capacious sac, 

 the large intestine. The latter is constricted behind and opens on the 

 surface as the anus, which has the form of a transverse slit and is pro- 

 vided with a sphincter muscle. Four Malpighian tubules open into the 

 anterior blind end of the small intestine and describe a few convolution^ 

 in the- dorsal body cavity. In the ventral body cavity lies a pair of less 



ready to pupate ; b, bristle-capped 

 tubercle of same ; c, head from 

 above. 



