168 ON TUBIFEX RIVULORUM. 



Such is Claparede's account of this curious organism, which, 

 if the reader would understand, he must carefully compare 

 with the figures illustrating this article, and with the worms 

 themselves, which may be easily obtained throughout the greater 

 part of the year. I will now give the most important of 

 Lankester's* views on this subject. He says, the structure and 

 position of the testes have not been fully made out by Claparede 

 and other writers. The young Tubifex, a quarter of an inch in 

 length, presents, in the ninthf fasciculate segment, a pair of pyriform 

 protoplasmic masses, very small, hanging one on either side the 

 nervous cord ; an exactly similar pair is seen in the tenth fascicu- 

 late segment ; the former are the testes, the latter the ovaries. 

 There is only one pair of testes, not two or three, as stated by 

 Claparede, who perhaps had not examined the youngest specimens. 

 . In the minutest details of structure the ovaries and the testes are 

 at this period identical, consisting of nuclei scattered in a common 

 protoplasm. After this period their development differs, for while 

 the ova increase individually, the young sperm-cells exhibit active 

 multiplication, by division of their nuclei into 2, 3, and 4, forming 

 floating, spherical, aggregates of very young sperm-cells, filling the 

 segment and dilating it into those adjacent as described by 

 Claparede. 



Lankester doubts Claparede's theory of the vas deferens being 

 invaginated in the oviduct, and says that the manner of oviposition 

 must be decided by further observation. He thinks also that the 

 seminal vesicle of Claparede is probably a cement-gland, and 

 contributes, together with the glandular wall of the vas deferens, to 

 the formation of the spermatophores which he has elsewhere 

 described. 



Reference has been made above to an Opalinoid Parasite, 

 which Claparede described as being frequently found in the seminal 

 receptacles, and this conducts us to, perhaps, the most interesting 

 part of this history. In another paper + Lankester gives reasons 



* Observations on the organisation of Oligochoetous Annelids, by Ray Lankester. 

 Annals Natural Hhiojy, 1871. 



+ This, it must be observed, is the tenth segment of the body, for the head is 

 devoid of setce. A discrepancy in this respect with CJlaparfede is at once apparent, 

 for he says the testes are in the ninth body segment, etc. 



X On the structure and origin of the Spermatophores of Tubifex, by E. Ray 

 Lankester, Quar. Journ. Mitr. Sci., 1871, Vol. i, p. 180. 



