1852.) OF THE ROYAL INSTITUTION. 187 
The Bipinnaria and the Starfish, are as much forms of the same 
individual as are the Pluteus and Echinus or the caterpillar and but- 
terfly; 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 intes- 
tinal canal of the Bipinnaria, developed one of its own; and this is 
exactly what takes place in the Gyrodactylus, whose singular de- 
velopment 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 Salpee, 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 homo- 
logy 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 shew, 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 Ge- 
nerations” 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 shewn by H. Miiller 
to have the power of detaching one of its arms (a result of gemma- 
tion) which then leads a separate existence as the Hectocotylus. 
Without a misuse of words, however, no one would call this a 
separate individual, 
In conclusion the Lecturer stated his own views thus : 
The individual animal is the sum of the phenomena presented by a 
