Nemaihelminthes. Class 1. Nematoda. 



159 



body, is composed of three sections : a muscular oesophagus^ which acts 

 as a pump, a peculiar intestine devoid of muscles, and a short 

 muscular rectum. The anus is on the ventral side, near the hind end 

 of the body. The central nervous system consists of a nerve-ring, 

 provided with ganglion-cells, running round the oesophagus ; several 

 nerves are given off from this, two of which are specially important, 

 one passing along the mid-dorsal, the other along the mid-ventral 

 line. The ventral nerve ends posteriorly in a small ganglion. As to 

 sense organs, the little tactile papillse, which are always 

 present anteriorly and posteriorly (the latter especially in the males), 

 must be mentioned ; in some free- 

 living Nematodes, small eyes 

 have been found at the anterior 

 end. The excretory ap- 

 paratus seems to be represented 

 by a pair of delicate tubes, which 

 traverse the lateral arose, and open 

 anteriorly upon the under surface 

 in a common aperture. The 

 genitalia, in the female, con- 

 sist of two long, coiled tubes, 

 which open by a short common 

 duct, rather anteriorly upon the 

 ventral surface. Each canal con- 

 sists of two regions, not sharply 

 demarcated, the ovary and the 

 oviduct; the latter is frequently 

 much distended in the gravid 

 female, and serves as uterus, or as 

 brood-pouch for the numerous ova. 

 In the male, testis and vas deferens 

 are represented by a single, as a 

 rule, long coiled canal opening into 



the rectum, which thus represents a cloaca. The canal exhibits 

 two parts, of which the vas deferens is the shorter and wider, the 

 testis the longer and thinner. The male is usually provided 

 with copulatory organs, one, or at most two, curved chitinous 

 needles, the so-called spicula, which lie in sacs opening 

 into the upper wall of the cloaca. In copulation, the spicula are 

 protruded through the anus and introduced into the female genital 

 aperture ; in some forms, the cloaca is everted at the same time {see 

 below for the special arrangements in Trichina and Sirongylus). 

 The female usually surpasses the male in size ; sometimes also, 

 other striking differences occur. The Nematodes, as a rule, lay 

 eggs enclosed in a thick shell ; frequently the development is con- 

 siderably advanced when the egg is laid ; not a few are viviparous. 



Fig. 120. Hind end of a male 

 Nematode, longitudinal section. Dia- 

 grammatic, cl cloaca, d gut, m retractor 

 muscle of the spicule, s sheath of spicule, 

 w body- wall. — Orig. 



