CRISTATELLA MUCEDO. 77 



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, Uke the 

 first, is again produced, which affords the point of departure for 

 another similar cycle." 



For my own part, I must confess that this doctrine of "alter- 

 nation of generations " appears to be very ingenious, but yet may 

 not be true. It depends upon starting with a perfect^ unisexual 

 zooid. Is it perfect ? Is it not rather an imperfect polypede, 

 confined within the coenoecium until it has reached maturity, with 

 digestive and generative organs all complete, and not till then 

 liberated into the outer world ? True, the earlier zooid is an 

 apparejitly perfect creature, vibrating its cilia and swimming with 

 rapid movements through the perigastric space ; but then it does 

 not leave the parent cell until it has reached the perfection of 

 reproductive faculties. The whole of this interesting question 

 resolves itself into the true conception of the so-called unisexual 

 zooids. If in their extremely minute and consequently undis- 

 covered anatomy they contain the elements of generative organs 

 too minute to be discovered by the most powerful glasses, does 

 not the whole of this system of alternation of generations fall to 

 the ground ? 



In conclusion, while this paper has dwelt largely upon the one 

 particular family of Cristatella, it has necessarily included also the 

 chief features of the class Polyzoa. Anyone who studies the 

 monograph of Professor AUman must be impressed with the very 

 small portion of it which refers especially to the beautiful family 

 of the Cristatellidce. With the exception oi Pedinatella, the stato- 

 blast of this family is unique. The family is also unique in 

 being devoid of ectocyst, or outer sac. It possesses a peculiar 

 under surface, which distinguishes it in a remarkable degree from 

 the other families, and which imparts to it the unique faculty of 

 locomotion, and, so far as I can gather, the reproductive faculties 

 of the family (which contains only one genus, Cristatella miicedo) 

 are only to be conjectured from the development of other fami- 

 lies. If it does produce polypedes by the resulting spermatozooids 

 of testis and ovary, at what stage of the parent life are they pro- 

 duced? None have been found in the winter months, and 



