GENEEATIVE OKGANS OF VEKMES. 



189 



ticula whicli project far into tlie cavity of tlie coelouij and often 

 extend tlirough several segments. As a rule there are several 

 (as many as four) testes in different metameres. There is generally 

 only one pair of ovaries. As these laterally-placed organs, just 

 like the testes, force their products, when a large quantity is 

 developed, through several metameres, they seem to surround the 

 unpaired testes (Tubifex). When the generative matters break off 

 from their point of origin they float in the coelom. In some 

 (Enchytrteus) a number of ovarian germs break off together in a 

 mass, of which one ovum only comes to maturity. 



The efferent ducts for the semen are formed from the already- 

 mentioned looped canals, a pair of which are, as a rule, converted to 

 this purpose : these generally undergo modifications in size. The 

 funnel-like internal orifice, just as in the case of ordinary looped 

 canals, lies in the next preceding segment. The canal continued from 

 it, which is generally distinguished by its large supply of cilia, passes, 

 after several coils, to the terminal portion, which opens to the 

 exterior; a large lobed glandular organ is attached to it. The 

 terminal portion anteriorly to its orifice forms an ampulla, into 

 which the tube is invaginated for some distance, and from which 

 it may be protracted, so that it serves as a copulatory organ. The 

 excretory ducts of the ova are either special oviducts, similarly derived 

 from modified looped canals, or they are functionally connected with 

 the seminal ducts. In this case the enlarged 



terminal portion of the latter consists of a ^.S^ 



double tube, the internal portion is the con- 

 tinuation of the seminal duct, and the external 

 portion which surrounds it, functions as an 

 oviduct. Branchiobdella also conforms to this 

 type. 



155. 



The generative system of the Chtetopoda 

 is very much like that of the lower division of 

 the Scoleina. Only in a few, however, does 

 hermaphroditism persist, and sexual separation 

 has become the rule coincidently with a more 

 free habit of life. The generative products 

 arise in the walls of the body-cavity, as is also 

 the case in the Gephyrea. As a rule, the 

 places at which the ova or the sperm is de- 

 veloped are merely distinguished by the pre- 

 sence of these products (Fig. 93, o) ; they have 

 no special characters, and are therefore dis- 

 tinguishable only at the time when they are 

 functionally active. They are developed at the 

 same points in the same genera or species; 

 thus, for example, in Eunice they lie at the 

 nerve-chord. In a few cases they are limited 



Fig. 93. A parapo- 

 dium of T o m o p t e r i s. 

 ss Scale-liko formations 

 of the integument, which 

 arise from two processes, 

 hom.ologous with the 

 ventral and dorsal para- 

 podia of other Annelids, 

 o Ovary : a collection of 

 cells from which the ova 

 are developed. 



sides of the ventral 

 to a small number of 



