THE LARVAL DEVELOPMENT. 



131 



four-limbed larva. The form whose ontogeny was examined by 

 Leuckart, P. taenioides, inhabits, in its sexual condition, the 

 nasal cavity of the dog. The eggs are laid in the nasal mucus, 

 and with this they reach the exterior. For the further development 

 of the embryo an intermediate host is necessary. This, in the 

 case of P. taenioides, is a rabbit, which, by swallowing the eggs, 

 introduces them into its stomach, where the egg-integuments 

 become detached and the larva set free. In P. proboscideum also 

 (Stiles), the early stages are similar to the above. The eggs of this 

 form are found in the lungs of the boa constrictor ; from the lungs 

 they pass into the intestine, where they are found in quantities 

 in the fa?ces, with which they leave the body. They, too, must 

 be swallowed by an intermediate host in order to develop further. 

 Stiles was successful in introducing them into mice. 



The larva, which has a blunt anterior, and a pointed posterior 

 end, i.e., which is sup- 

 plied with a tail, has 

 two pairs of truncated 

 limbs, provided wuth 

 chitinous claws fur- 

 nished with a sup- 

 porting apparatus 

 (Fig. 58 C, and Fig. 

 59, st). The two claws 

 are attached to a 

 chitinous ring, and 

 seem to be quite in- 

 dependent of the 

 supporting apparatus. 

 This structure sug- 

 gests that the limb 

 consists of a terminal, 

 and a basal seg- 

 ment, the limb being 

 thus regarded as two- 

 jointed. Stiles, who 

 adopts this view, 

 thought the limb more distinctly marked off from the body than 

 did Leuckart, who regarded it as consisting of one joint only. 



At the anterior end of the body lies a boring apparatus composed 

 ■of several chitinous spines (Fig. 59, ba), which has been compared 



Fig. 59. — Quadrupedal larva of Pcntastomum proboscideum, 

 from the ventral side (after Stiles), ba, boring apparatus ; 

 dst, stigma of gland ; dz, gland - cells ; kr, claws ; to, 

 mouth ; ma, stomach ; n, rudiment of the nervous system ; 

 oes, oesophagus ; ^',-j'o, truncated limbs; ro, dorsal organ, 

 seen through the transparent body ; s, caudal appendage ; 

 st, apparatus for supporting the claws ; tp, sensory papillae. 



