372 THE NATURAL HISTORY REVIEW. 



stock. The ova and spermatozoa are likev^ise then developed, and we 

 find females with their bodies entirely filled with ova while they are 

 still attached to the parent stock, while in this latter in its 12 anterior 

 rings not the least traces of ova or spermatozoa are to be found ; in 

 the males it is only the anterior rings that are filled with spermatozoa. 

 The parent stock secretes a case for itself on the stems of some 

 Campanularia and with the sexual zooid still attached, moves freely 

 about, leaving its case and returning to it. The male and female 

 after they have separated from the parent stock do not build cases, 

 but creep along the stems of Campanularias and are often to be found 

 swimming about. 



The general appearance of the male is entirely difierent from that of 

 the female. The body, instead of tapering gradually from the middle 

 towards both extremities, attains its greater width much nearer the 

 head, the number of rings provided with long setae, and having short 

 dorsal cirri are five instead of six. The spermatozoa are found on the 

 sides of these five rings only, but they never, as in the case of the ova 

 in the female, extend throughout the whole cavity. The two large 

 tentacles, instead of being simple, of the same breadth, and rounded at 

 their extremities, are very broad at their base, where they are united 

 by a prolongation of the anterior part of the head. At a short distance 

 from their base they bulge out, but without actually meeting, and 

 they then divide into two branches at their extremity. The median 

 tentacle is much larger than that of the female, and directly behind 

 the eyes there is an additional small cirrus. 



We thus see that from a fertilized ovum a form is produced which 

 having passed through a certain number of stages, at last reaches 

 what we may call an adult existence, that this form is asexual, but 

 that by means of a process of prolification it gives origin to one or 

 several sexual zooids, which are either male or female, and which in 

 their turn produce what A. Agassiz calls ' parent stocks.' If we 

 compare the embryonic development of the parent stock from the 

 ovum with that of the male and female zooids from the parent stock, 

 we cannot fail being struck with the perfect coincidence that exists 

 between the development of the parts of the head and of the dorsal 

 cirri in both. In the parent stock the alimentary system is more 

 highly diff'erentiated. The generative system is thrown off" as it 

 were, in the form of male and female zooids, destined to live but for 

 a brief period, and more locomotive than the parent stock— which on 

 the separation of a zooid, forms by means of budding, new rings ; and 



