OTHER FORMS OF ALTERNATION. 175 



nation prevails, still tlie great amount of apparent diversity 

 seems to call for some enquiiy into the causes to which tliis 

 may be due. These appear to be mainly the two following : — 



1. The detachment of the parts of reproduction from the 

 organism producing them, much in the same way that the 

 typical form is separated as a free zooid from the original 

 germ-mass, in the protomorphic form of alternation. 



2. The development, in connection with these parts of 

 reproduction, of accessory organs of alimentation, locomo- 

 tion, &c. 



From the influence of these processes on the gcnenil or- 

 ganization, the phenomena of reproduction are, in many 

 cases, made to assume a character as unlike that of the 

 higher animals as can well be conceived ; but the instances 

 of transition forms just noticed are sufficient to show that 

 differences in these points cannot be allow^ed any weight in 

 determining for or against their essential community "f 

 nature. 



In regard particularly to what may be termed the adven- 

 titious organization of the reproductive zooids, as com- 

 pared with mere organs fulfilling the same function, thi« 

 conclusion is strengthened by the contrast of phenomena 

 of an opposite kind — the degradation of individuals in cer- 

 tain species to the position of mere sexual mechanisms. 

 Wonderful, as it undoubtedly is, to find the homologues of 

 the reproductive organs at times so elaborately organized as 

 to present the characters of distinct animals, and even to 

 simulate species higher in the scale than those of which 

 they are really but detached members, it is not perhaps 

 more wonderful than to meet with animals of undoubted 

 zooloo'ical distinctness — as the males of some Rotifera and 

 Cirripedia — whose organization seems almost limited to tlie 

 parts required for the performance of the sexual function.* 



♦ From the observations of Mr. Gosse in the Phil. Traus. for 1837, it 



