THE LARVAL DEVELOPMENT. 



133 



infection, in the cysts of P. taenioides, besides the worm-, or, rather, 

 maggot-shaped larva, two cast integuments, on which could be 

 distinguished remains of the embryonic chitinous structures, viz., 

 the dorsal cross and the chitinous oral horseshoe-shaped band, and 

 probably also the remains of the truncated limbs. Several further 

 moults then take place, a long time being occupied by this develop- 

 ment ; five to six months, according to Leuckart, pass before the 

 larva of P. taenioides attains its full development in the intermediate 

 host. The development of P. 2^'oboscideum is somewhat more rapid, 

 but also occupies several months (Stiles). 



While the larva remains in the cyst, and during the course of 

 several moults, the most important change which takes place is the 

 development of the internal organs; the external form, however, 



ov. 



s?iu^ 



ma- 



Fig. 61. — Encysted female larva of Pentastomum taenioides from the viscera of a rabbit, about 

 four months after infection (after Leuckart). a, anus ; ed, proctodaeum ; Ih, larval integu- 

 ment (detached cuticle) ; m, mouth ; ma,, stomach ; mu, retractor muscles of the pharynx ; 

 n, nervous system ; od, oviduct : oe, genital aperture ; oes, oesophagus ; or, ovary ; tn, nerve 

 running from the oesophageal ganglion to the tactile papillae ; vwj, vagina. 



also undergoes a few changes, to be described below. The internal 

 organs of the free larva, as far as could be ascertained, seem to pass 

 direct into those of the encysted larva and of the sexually mature 

 animal. The intestinal canal, which was not extensive in the free 

 larva, widens and becomes differentiated into its separate regions, 

 pharynx, oesophagus, and stomach. The latter soon becomes very 

 large (Fig. 60, ma). It ends blindly posteriorly, and only becomes 

 connected later with the proctodaeum (ed). 



The accumulation of cells round the oesophagus present in the 



