320 



ZOOLOGY 



the former opens into a sac, which can be everted so as to form a proboscis or 



introvert, and is armed with spines. The enteric canal consists of a muscular 



pharynx and a straight intestine. A pair of 



sacs opening by ciliated ducts on the tenth 



segment appear to be excretory organs. The 



sexes are separate : the gonads are paired sacs 



opening at the posterior end of the body. 



3. Family Desmoscolecidaz. 



Desmoscohx is also a minute marine worm, 

 having a globular head and a variable number 

 of segments (Fig. 262). The head bears four 

 movable chitinoid rods or setse, and a pair of 



Fig 261 . Echinoderes, x about 210. 6, spine ; 

 c.s. caudal spine ; ph. pharynx ; s. and s'. spines 

 on the proboscis ; s.g. salivary glands ; at. stomach. 

 (After Hartog.) 



Fio. 262.— Female Desmoscolex, 

 ventral view, x 260. a, ovary. 

 (From Shipley, after Panceri). 



similar structures occurs on many of the other segments. The terminal mouth 

 leads by a muscular pharynx into a straight intestine : the anus is dorsal in posi- 

 tion. The animal is dioecious ; the gonads have the form of simple sacs, the testis 

 opening along with the anus, the ovary on the ventral surface anterior to the 

 anus. The male has a pair of penial seta?. 



AFFINITIES AND MUTUAL RELATIONSHIPS OF THE 

 NEMATHELMINTHES. 



The affinities of all the classes of Nemathelminthes are very 

 obscure, and the propriety of grouping them into a single plvylum 

 is extremely doubtful. They all agree in being elongated, cylin- 

 drical worms with a body-cavity, which is sometimes of the 

 nature of a true coelome ; there is a certain resemblance 



