ASCARIS 



135 



the front end is the mouth, guarded by three Ups, one above and 

 one at each side below. The dorsal lip bears at its base two papillae 

 and the ventro-lateral lips one each. The edges of the lips bear 

 many small teeth, those of suillcB being smaller than those of 

 lumhricoides . Median on the under side, about two millimetres 

 from the mouth, is a so-called ' excretory ' pore. The female 

 bears a median genital pore at about one-third of the length 

 of the body from the front end, on the ventral side of a region 

 which is slightly narrowed. The tail is curved downwards, 

 slightly in the female and strongly in the male. The anus lies 

 below, about a couple of millimetres from the hind end. In the 



Fig. 98. — Ascaris lumhricoides. — From Sedgwick, after Leuckart. 



a, Hind end of male ; b, head, from above ; c, head, from below ; d, egg, in shell ; p, ' excretory ' pore ; 



Sp, penial setae. 



male this opening serves also as a genital pore, and there project 

 from it a pair of penial setae. 



Internally, a spacious perivisceral cavity separates a straight, 

 simple gut from a simple body-wall. The cavity is traversed by 

 numerous delicate strands of a remarkable connective tissue, 

 which is composed of processes of a few cells, notably of one very 

 large cell placed on the dorsal side just behind the nerve ring. 

 Over the gut and the muscle fibres of the body-wall the strands 

 join a thin covering layer which lines the cavity. Thus the body 

 cavity may be regarded as intracellular, and is thus unlike 

 that of other animals, which is either coelomic or haemocoelic 

 (p. 188). 



The body-wall is made up of three layers (Fig. 99) : a stout, 

 smooth cuticle, made of the protein collagen with some keratin, 

 which consists of several layers and is shed four times, an ecto- 

 derm (' hypodermis ') which is without cell-limits and must 

 therefore be classed as a syncytium (p. 35), and a single layer of 

 peculiar muscle fibres. The body-wall contains a peculiar form 



