Il6 AXATOMY AND DEVELOPMENT OF THE ECHINODERMS 



embryo cells of the ovum, and which as such, retain a portion of the 

 original " spermatic force," whence they are enabled to attain a certain 

 independent development \\-ithout a renewal of the spermatic 

 influence. 



Now the questions to be decided before the alternation theory can' 

 be said to apply to the Echinoderms or any other animals, are different 

 as regards the two portions of the theory. The problem as regards 

 the first question is a matter of naming — as regards the second it is a 

 matter of fact. 



We have said that the question involved in the first part of the 

 theory is a question of naming. It is, whether we can apply to A, B, C, 

 &c. in the foregoing instance, the name " individual." For it is quite 

 clear that if they cannot with propriety be called " individuals,'' their 

 succession cannot be called an " alternation of eenerations,'' inasmuch 

 as generations are composed of individuals. 



We must carefully bear in mind that this inquiry has nothing to do 

 with the thorny problem of psychical individuality. With that the 

 zoologist has no concern ; his science investigates the laws of animal 

 form, and in psychological questions he has no more direct interest 

 than the astronomer has in the zoology of the planet Saturn. 



Leaving psychological considerations aside, then, and inquiring 

 into the zoological meaning of the term " individual," we find that anj-- 

 thing to which it is applied among the higher and the greater part of 

 the lower animals, has \.\\o principal characters : first, it has an inde- 

 pendent existence ; and secondly, it is the total result of the independent 

 development .of a single ovum. 



Now the forms A, B, C, described as " individuals " by Steenstrup,. 

 have only one of these characters (in the most stronglj^ marked cases 

 of " alternation "), that of independent existence ; for each of them is 

 owXy part of " the total result of the development of a single ovum." 



But in predicating " individuality " of an}' animal which does not 

 '' alternate," we predicate both these characters of it. 



Hence, unless the meaning of the term " individual " be altered, 

 the advocates of the alternation theory commit the capital error of 

 using the same term in two very different senses, according as the}- 

 speak of a Hydra or a Campanularia, a Salpa or a Cynthia. 



It is only by narroA\ing the meaning of the word " individual " to 

 mere " independent existence," that it can possibly become applicable 

 in Steenstrup's sense. But in this case spermatozoa, spermatophora, 

 and even cancer cells, ^^•ould equally be " individuals." So that the 

 new meaning would be not only entirely arbitrary, but opposed to the 

 general sense of zoologists. 



