42 ALTERNATION OF GENERATIONS. 



much more highly differentiated structure, in which the organs of digestion especially hold 

 a dominant position, and which we may regard as sexual or non-sexual, according to the view 

 we take of the relation between it and the testis, as will presently be seen. 



Now, if the formation of the ovary be attended to, it will be seen that this body is 

 developed at a late period from the walls of the original sac-like embryo, which have under- 

 gone slight changes, and have become the endocyst of the more mature Polyzoon ; and it will 

 be at once perceived that this development of the ovary takes place in a way which may 

 obviously be compared with the formation of a bud ; that at least in Alcyonella it occupies 

 exactly the position in certain cells that the buds destined to become polypides do in others, 

 and that at an early stage of polypide and ovary it is scarcely possible to distinguish one from 

 the other; so that the idea is immediately suggested, that the body here called ovary is itself 

 a distinct zooid, in which the whole organization becomes so completely subordinate to the 

 reproductive function as to be entirely masked, and apparently replaced by the generative 

 organs. This would then constitute a third zooid, which would therefore be a sexual zooid ; 

 it is, however, unisexual (female). 



In the next place we find that upon the funiculus (in Alcyonella), which probably belongs 

 rather to the polypide than to the endocyst, there is developed the mass here described as 

 testis. Now, if we view this mass as a mere organ of the polypide, we must then regard the 

 latter as the second sexual or male zooid ; but the testis may perhaps be more correctly 

 considered, like the ovary, as a distinct sexual bud, having the generative system so enor- 

 mously predominant as to overrule and replace all the rest of the organization ;* this bud, 

 like the ovary-bud, being also unisexual, but with a male function. In confirmation of this 

 view, it is to be remembered that the funiculus has the power of giving origin to a very 

 remarkable form of undoubted bud, the statoblast, which, until ulterior development is excited 

 in it, has no nearer resemblance to an ordinary polypide-bud than the testicular mass has; 

 and to this statoblast — so far at least as position is concerned — the male bud or testis in 

 Alcyonella would therefore be related just as the female bud or ovary is related to an ordinary 

 polypide-bud. In Paludicella the testis, though in immediate connection with the funiculus, 

 is developed apparently from the endocyst. 



If the above be the correct view, the complete comprehension of the Polyzoon will involve 

 the conception of a ciliated sac-like embryo as a starting point, and a series of buds, of which 

 the last term will consist of a pair of sexual buds, the others being non-sexual ; from the 

 sexual buds a true embryo like the first is again produced, which affords the point of 

 departure for another similar cycle. 



* Analogous instances of the dominant development of the generative system, so as to suppress 

 more or less completely the development of all the other organs, occur in other members of the animal 

 kingdom ; as examples, may be mentioned the reproductive capsules (true buds) in certain Polypi, and 

 the male of some of the Rotiferce. 



