210 



ANNELIDA. 



oviducts, which just before their termination at the lateral openings 

 (c) become thick and glandular. These animals most likely co- 

 pulate like the earthworm, and lay their 

 eggs in a similar manner. We have al- Fig. 86. 



ready seen in the Lumbricus terrestris 

 ova containing two yolks, 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 enclosing 

 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 

 separately from the ovaria, and remain 

 distinct from each other as they pass 

 along the tortuous canal which leads to 

 the external opening ; but at length, ar- 

 riving at the thick and glandular portion 

 (c) of the oviferous tube, several of them 

 become enclosed in a common investment 

 secreted by the walls of the oviduct, and 

 are expelled from the body with the out- 

 ward appearance of a simple egg. 



(253.) Besides the ordinary mode of pro- 

 pagation by ova, it has long been ascertained 

 that some of the Annelida at least are re- 

 produced by spontaneous division. Bonnet, M tiller, and Duges, all 

 agree that this is the case with certain species of Nais ; and in Nais 

 filiformis the process of separation has been witnessed from its com- 

 mencement to its termination. The division was seen to occur 

 near the middle of the body of the animal, the posterior half re- 

 maining motionless upon the mud of the bottom of the vessel, 

 whilst the anterior portion buried itself as usual ; after some days 

 the truncated extremity of the hinder part was observed to become 

 swollen, transparent, and vascular, and ultimately to assume the 

 complete structure of the mouth of the perfect animal ; it then 



* Duges, loc. cit. 



