242 



ANNELIDA. 



vermiform bodies are seen to float, and most probably represents the 

 testis. The twelfth segment likewise exhibits two openings, each placed 

 upon the centre of a little nipple (c) : these arc the orifices leading to 



Fig. 117. 



the female portions of the sexual system. 

 The ovaria (d, e) are composed of four large 

 and several smaller masses of a granular 

 character ; and from them proceed long and 

 tortuous oviducts, which, just before their 

 termination at the lateral openings (c), 

 become thick and glandular. These animals 

 most likely copulate like the Earthworm, 

 and lay their eggs in a similar manner. 

 We have already seen, in the Lumbricus 

 terrestris, ova containing two yelks, and 

 consequently giving birth to two animals ; 

 but in the Nais every egg produces ten or 

 a dozen young ones * ; or perhaps we ought 

 rather to say that what appears to be a 

 single egg is in fact merely a capsule en- 

 closing several distinct ova, from which a 

 numerous progeny arises. The manner in 

 which these compound eggs are formed is 

 easily understood when we consider the 

 structure of the oviduct described above. 

 The granular germs escape, no doubt, sepa- 

 rately from the ovaria, and remain distinct 

 from each other as they pass along the 

 tortuous canal that leads to the external 

 opening; but at length arriving at the 

 thick and glandular portion (c) of the ovi- 

 gerous tube, several of them become en- 

 closed in a common investment secreted 

 by the walls of the oviduct, and are expelled from the body with the 

 outward appearance of a simple egg. 



The account of the reproductive system of the Naides given by Dr. 

 Williamst is as follows : 



(63o.) In Nais serpentina, which may be taken as the type of the 

 genus, two of the ' segmental organs ' are present in every ring of the 

 body, one on either side of the intestine. Each organ commences (or, 

 if the course of the contained current be considered, ends) in a single 

 external orifice. At its free internal extremity it is held in a determi- 

 nate position by means of bridles of delicate threads. By the action of 

 large and vigorous cilia, a strong current of fluid is drawn into this open 

 mouth. From the form and structure of the trumpet- shaped extremity, 

 '* Duges, Ann. des Sci. Nat. vol. xv. f Phil. Trans. 1858. 



Generative organs of Nais. 

 (After Dugbs.) 



