OTHER FORMS OF ALTERNATION. 177 



animal ; in the other we have a true animal, so far below 

 par in its structural development as to resemble a mere 

 organ. The contrast shows in a striking way that the sup- 

 pression of normal parts in an animal, or the development 

 of adventitious structures in connection with any particular 

 organ, are not of essential importance in determining what 

 has been termed by some authors " zoological individu- 

 ality." 



The other character the detachment of the sexual 

 structure is not, as it would seem, of more importance 

 than its amount of organization, allied species both of Poly- 

 pifera and of Cestoid worms differing among themselves in 

 this respect. It is even said that in some Tubularian 

 polypes there occur in the same species both sporosacs and 

 medusoids.* 



It may be mentioned, too, that even so high in the scale 

 of organization as among the Decapod Crustaceans, we meet 

 with something analogous to the elaboration of the repro- 

 ductive corpuscules after their envelope has become de- 

 tached, for in the case of certain crabs it would seem that 

 the spermatozoa are not fully matured till after the vesicles 

 in which they are formed have been introduced into the 

 sperinatheca of the female. f 



In fact the whole question of detachment hinges on the 

 proportionate development of the somatic life, i.e., the life 

 of the body as one whole, and the more or less independent 

 life of its several organs, or what we may term the topical 

 or regional life. In the higher animals the special actions 

 of the several organs are as completely subordinated to that 

 of the body as a whole, as are the powers of local corpora- 

 tions to the central government in any well-ordered state, 

 yet there still remains sufficient evidence of the real exist- 



* Carpenter's Comparat. Physiol., 4th Ed., p. 552. 



f Goodsir's Anatomical and Pathological Observations, p. 39. 



i 3 



