28 
HISTORY OF ZOOPHYTOLOGY. 
lability, — the existence of a mouth and stomach, — the nature of 
their food, its digestion, and the evomition of the indigestible 
remains are incontestible proofs of this ; — and it seems impro- 
bable, to say no more, that this animal should be fitted round 
with a case that grew independent of it and from a different 
cause. And the case itself has no analogy, as Ellis shewed very 
clearly, either to bark or to wood : it possesses the structure of 
neither of them, nor is it formed in the same manner by the 
addition of concentric layers, nor does it contribute to the 
formation of new parts, but, like the shell of testaceous mol- 
lusca, it is extravascular, and when once formed suffers no 
other change than what external injuries or time may operate. 
If possible its coincidences with the skin of cellular plants are 
even fewer : the one is a living part which has very important 
functions to perform in relation to the plant itself and to the at- 
mosphere or circumfluent medium in which it lives ; the other 
exhibits no action characteristic of life, and is nothing more 
than a condensed albuminous or calcareous sheath, appropriat- 
ed solely to support or protection.* 
But although I agree with the advocates of the animality of 
zoophytes in general, I cannot go the length of Ellis in consi- 
dering it proved that sponges and corallines belong to the same 
class. Ellis, we have seen, knew that no polypes were to be 
found in sponge, and their existence in the pores of corallines 
was inferred merely from the structure of these and their chemical 
composition. They have been examined by subsequent natu- 
ralists fully competent to the task, and under the most favour- 
able circumstances, — in particular by Cavolini and Schweigger, 
— and the result has been a conviction that these productions 
are truly apolypous. Now this fact, in my opinion, determines 
the point, for if they are not the productions of polypes, the zoolo- 
gist who retains them in his province must contend that they are 
individually animals, an opinion to which I cannot assent, see- 
* I do not enter into the question whether the Confervse are real animals or 
not, because, whatever conclusion we might adopt, they would not come within 
our definition of a zoophyte or polype, since they assuredly have neither mouth, 
tentacula, nor stomach. Nor need I discuss the propriety of instituting, with 
Treviranus, a fourth kingdom of animated nature, composed of the zoophytes 
and aquatic cryptogamia, as my object and plan is only to describe what have 
been almost universally considered zoophytes. 
