322 MOLLUSCOUS ANINALS. 



understand the perceptions on these subjects of the man who fancies 

 them separated by the same kind of distinctions as either of them and 

 any Articulate. It is true we must not expect that all our groups, 

 even those which we place in equal rank, should have equally im- 

 portant and well-marked characters ; but we surely ought to be able 

 to distinguish between difference of general plan and difference in the 

 mode of carrying it out, or in the grade of development. I cannot 

 but think that the eminent naturalists who insist on the separation 

 we are considering, do really perceive and admit, as indeed the name 

 they have employed conveys, the peculiarly close relationship of 

 Mollusca and Molluscoida, but they fancy the distinction may assist 

 the student and they do not attach the kind of importance which we 

 do to the grand differences of plan amongst organised beings. They 

 are probably of those who regard all classification as a mere human 

 contrivance intended to aid our judgment and memory, but having no 

 connection with the realities of nature ; whilst to us, it is an attempt 

 at the true interpretation of the Divine plan and not a record merely, 

 but an embodiment of the knowledge gained of the real relations of 

 organised beings. To us it appears that the five sub-kingdoms 

 express the great fact that five distinct plans of structure are manifest 

 in the animal kingdom, and unless we were brought to perceive 

 another plan as distinct as any of these, which, we believe, no one will 

 pretend to have found, we could admit no alteration in the general 

 outline of the animal kingdom which has been so clearly marked out. 

 I might add that no clear definitions of the proposed separate sub- 

 kingdoms have been laid down, and that it is even left doubtful where 

 the line should be drawn. I do not think, however, that further 

 discussion of this point can be needed. We will proceed to speak of 

 the relations of the Mollusca with the other sub-kingdoms ; and here 

 it is obvious that, whilst a gradation is observable from highest to 

 lowest, relations of some parts of each to parts of the others are 

 equally manifest. It is also to be noticed that in each sub-kingdom 

 there is a gradation from the highest condition which the common 

 type allows to the lowest that is at all consistent with it. Thus, for 

 example, the lowest vertebrates are considerably inferior to the greater 

 number of Articulates, Mollusks and even many Radiates ; and there 

 are members of even the highest class of Articulates which, though 

 their type is sufficiently perceived, are in actual development scarcely 

 raised above Protozoa. There can be no doubt of Vertebrata occupy- 



