176 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



according to the criterion of individuality adopted. But it 

 does serve to emphasize the justice of Huxley's (1851) 

 contention, that the zoological individual is "The sum of 

 the phenomena successively manifested by, and proceeding 

 from, a single ovum, whether these phenomena be invariably 

 collocated in one point of space or distributed over many." 



This conception was arrived at from the embryological 

 and comparative zoological point of view, as the only means 

 of homologizing the various colonies and pseudo-individuals 

 found among the invertebrata with what we have been 

 accustomed to call the individual among the mammals. It 

 is best spoken of as the biological individual. 



But the above conception of the biological individual does 

 not include all of the attributes of what we usually mean by 

 an individual. We may still have the morphological and 

 physiological individual — an individual localized in a single 

 mass and functioning as a coordinated whole. Both of 

 these conceptions are united in the individual as seen among 

 mammals; but they may be separated, and when this is the 

 case, which is the more essential ? Although this question 

 must always remain more or less a matter of opinion, these 

 observations on Botryllus show that the conception of the 

 biological individual is more than a mere generalization 

 from embryological and comparative data. For, in this 

 case, the isolated pieces of the biological individual always 

 retain a latent physiological individuality, by means of which 

 they can recognize each other (so to speak) and thus 

 cooperate instead of competing with each other when they 

 are again brought into contact. Ordinarily there is no such 

 compatibility between different biological individuals. The 

 fact that sometimes, however, fusion is observed between 

 related biological individuals does detract somewhat from 

 the value of this argument, and also shows that since two 

 biological individuals may form a single physiological one, 

 under perfectly natural circumstances, it is difficult to apply 

 the usual conception of the individual to the lower animals. 



To pass on to the second question, namely, To what 

 extent should a Botryllus colony be considered as a single 



