28 HISTORY OF ZOOPHYTOLOOY. 



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 aorree with the advocates of the animalitv 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 Confervae 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 dcscrihe what have 

 been almost universally considered zoophytes. 



