i8o 



ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. 



be looked on as a very primitive kind of nerve, as it passes straight to 

 the dorsal or ventral line and forms a direct bridge connecting the 

 longitudinal nerve trunk with the myo-epithelial cell. 



Traversing the axis of the body is the alimentary canal which is very 

 simple in structure in correlation with the fact that the Ascaris lives 

 amongst food-material which is digested for it by its host. The mouth 



d.l. 



in^. 



v.l. 



Fig. 82. 



Ascaris (?), transverse section, c, Cuticle; d.l, dorsal line; ep, epidermis; ex, excretory tube; 

 inl, intestine ; l.l, lateral line ; m.e, myo-epitlielial cell ; od, oviduct ; ov, ovary ; t, tail of myo- 

 epithelial cell ; ut, uterus ; v.l, ventral line. 



(Fig. 81, in) is a small pore at the tip of the body, surrounded by three 

 roundish lobes arranged like a trefoil, one lobe being dorsal and the other 

 two ventral. The mouth leads into a short pharynx with thick walls 

 and this in turn leads into the thin-walled intestine which passes without 

 a break to the anus — a transverse slit on the ventral side close to the pos- 

 terior end of the body (Fig. 81, an). The wall of the intestine (Fig. 82, int) 



