UPON ANIMAL INDIVIDUALITY 1 49 



The Bipinnaria and the Starfish are as much forms of the same 

 individual as are the Pluteus and Echinus, or the caterpillar and 

 butterfly ; but here the development of one form is not necessarily 

 followed by the destruction of the other, and the individual is, for a 

 time at any rate, represented by two co-existing forms. 



This temporary co-existence of two forms of the individual might 

 become permanent if the Asterias, instead of carrying off the in- 

 testinal canal of the Bipinnaria, developed one of its own ; and this 

 is exactly what takes place in the Gyrodactylus, whose singular 

 development has been described by Von Siebold. 



But the case of the Gyrodactylus affords us an easy transition to 

 that of the Trematoda, the Aphides, and the Salpae, in which the 

 mutual independence of the forms of the individual is carried to its 

 greatest extent ; so that even on anatomical grounds it is demon- 

 strable that the difference between the so-called " skin " of the 

 caterpillar, the free Bipinnaria, and the Salpa democratica is not in 

 kind, but merely in degree. 



Each represents a form of the individual ; the amount of inde- 

 pendent existence of which a form is capable cannot affect its 

 homology as such. 



The Lecturer then proceeded to point out that the doctrine of the 

 " Alternation of Generations," and all theories connected with it, rest 

 upon the tacit or avowed assumption " that whatever animal form has 

 an independent existence is an individual animal," a doctrine which, 

 he endeavoured to show, must, if carried out, inevitably lead to 

 absurdities and contradictions, as indeed Dr. Carpenter has already 

 pointed out. 



There is no such thing as a true case of the " Alternation of 

 Generations " in the animal kingdom ; there is only an alternation 

 of true generation with the totally distinct process of Gemmation 

 or Fission. 



It is indeed maintained that the latter processes are equivalent to 

 the former ; that the result of Gemmation as much constitutes an 

 individual as the result of true Generation ; but in that case the 

 tentacles of a Hydra, the gemmiferous tube of a Salpa, nay, the legs 

 of a Centipede or Lobster, must be called individuals. 



And if it be said that the bud must have in addition the power 

 of existing independently to constitute an individual, there is the 

 case of the male Argonaut, which has been just shown by H. Miiller 

 to have the power of detaching one of its arms (a result of gemmation), 

 which then leads a separate existence as the Hectocotylus. 



