ON TUBIFEX KIVULORUM. 173 



of the receptacle would be to escape into the water and be lost. 



The only other hypothesis is, that they permeate the wall of 

 the receptacle into the perivisceral cavity of the tenth segment, 

 and thence find their way into the eleventh, and so fulfil their 

 function. In the course of this transmigration they would inevit- 

 ably become intermingled with the spermatozoa proper to the 

 worm, a result which seems equally difficult to admit. Further- 

 more, a question arises, and a most interesting one, as to the 

 function of the spermatophore. We find these objects, as I have 

 lately had occasion to describe in the case of one of the 

 Entomostraca, viz., Diaptomiis Castor,^ to be carriers of the 

 seminal fluid, attached by the male to the female. But in the 

 present case they are clearly not, as in the former, a means of 

 transmission, inasmuch as they are formed from the seminal fluid 

 within the female organs of the worm after copulation has taken 

 place. It has been suggested to me that their office may be to 

 detain the spermatozoa, and thus to regulate their diffusion in 

 correspondence with the ripening of the ova in the next segment. 



The ova, upon their expulsion, are found four or five together 

 in tough leathery capsules, see Fig. 1 6, having a projection at either 

 end. The course of their development has been described by 

 d'Udekem as follows : — As soon as the eggs leave the body, they 

 lose the germinating vesicle, the yelk divides into two, then into 

 four, and when this division has resulted in a mulberry mass, a 

 transparent zone is formed around it, which is the blastoderm, 

 and which may be rendered clear by the addition of acetic acid. 

 The blastoderm is composed of minute cells, and subsequently is 

 divided into two layers, the external forming the integument, and 

 the internal the alimentary canal of the young animal; the embryo 

 with its various organs is then gradually formed. The projections 

 at the poles of the capsule are softer than at the other parts, and 

 here the young escape. They differ from the adult chiefly in the 

 number of the segments, and the absence of the genitalia. A 

 week suffices for the development of the eggs. Growth consists 

 not in the addition of new rings, but in the sub-division of the 

 last one. 



* In a recent note-book of the P. M.S. 



