GENERATIVE ORGANS OF VERMES. 



185 



double character of these parts. But this would also be the result if 



the two tubes were separated froui one another in adaptation to the 



elongated form of the body. The blind terminal 



portion of the generative tubes serves as an ovary 



or testis, the remaining portion as an efferent organ, 



adapted to different arrangements in different parts, 



and variously differentiated. 



The male generative tube is a simple one, open- 

 ing on the ventral face of the hind-gut ; in the larger 

 species it is several times coiled. It is only by its 

 epithelial investment that the terminal portion, 

 which is generally of some length, is distinguished 

 from the excretory duct, and seen to be a testis ; a 

 widened portion, or seminal vesicle of the ductus 

 ejaculatorius, is sometimes added to the duct. Two 

 fine, and sometimes very long, chitinous rods 

 (spicula) are developed in the cloacal portion of the 

 hind-gut, and serve as copulatory organs. 



The female generative tubes are, as a rule, 

 double, and are either separate, except at their 

 orifice, or have their terminal portions united into 

 a common tract. The tubes are more or less 

 coiled, according to their length. The terminal 

 portion is to be*regarded as an ovary (Fig. 88, ov), 

 from which a portion which is ordinarily wider leads 

 into a canal known as the uterus {u), and this opens 

 by a nan'ow vagina. The female generative pore 

 is always ventral in position, in front of the anus, 

 and generally about the middle of the long axis of 

 the body. The increase in number of the female 

 generative tubes to five, with the atrophy of one 

 of the two primitive ones, gives rise to changes in 

 the form of the apparatus : this is more marked 

 when particular regions are specially differentiated. 

 The same thing happens to the male organs. In 

 some cases the terminal portion of the ovary func- 

 tions as a yelk-gland (Leptodera). 



Mermis, at any rate, among the Gordiacea, re- 

 sembles the other Nematodes in the characters of 

 its generative organs. In Gordius the excretory 

 ducts of the paired germ-glands are, in both sexes, 

 united with the hind-gut. This happens in male 

 Nematodes only. 



In the ChaBtognathi (Sagitta) the arrangement 

 is somewhat different ; owing to their hermaphro- 

 ditism, and the way in which the organs are dis- 

 posed, we cannot compare them very closely with other divisions. 

 The male and female generative glands lie at the sides of the pos- 

 terior ends of the body ; the testes lie behind the ovaries, and 



Pig. 89. A Sa. 

 gitta with its 

 generative organs. 

 Ovary, t Testes. 

 s Seminal vesicles. 

 i Enteron. p Fins. 



