314 



ZOOLOGY 



SECT. 



separate. The male has a single testis : the vas deferens opens along with 

 the anus : there are two penial setae. The female has paired ovaries and a 

 single vagina opening near the middle of the body on the ventral side. 



2. Family Echinoderidce. 



EcMnoderes is a minute marine worm of cylindrical form with a flattened 

 ventral surface. The body is segmented, or divided into rings, eleven or 

 twelve in number, all strongly cuticularised, and most of them bearing spines 

 (Fig. 266). The mouth is placed at the anterior, the anus at the posterior 

 end of the body : 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 Desmoscolecidee. 



Desmoscolex is also a minute marine worm, 

 having a globular head and a variable number of 

 segments (Fig. 267). The head bears four movable 

 chitinoid rods or setae, and a pair of similar struc - 

 tures occurs on many of the other segments. The 

 terminal mouth leads by a muscular pharynx into 

 a straight intestine : the anus is dorsal in position. 



U- 



FIG. 206. Echinoderes, x about 210. b. spine ; 

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

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

 (After Hartog.) 



FIG. 267.- Female Desmoscolex, 

 ventral view, x 260. a. ovary. 

 (From Shipley, after Panceri.) 



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?. 



Trichoderma has some superficial resemblance to Desmoscolex, but is nearer 

 the ordinary Nematodes. 



