70 MOLLUSCOUS TYPE OF STRUCTURE. 



on the two sides of the head being made up of a vast number 

 (often many thousands) of minute eyes, every one perfect in 

 itself (ANIM. PHYSIOL. 573). The possession of these com- 

 pound eyes is so characteristic of the Articulata, that any animal 

 in which they were found, might be unhesitatingly referred to 

 that series. 



48. The characters that have been enumerated are very 

 far from being all, which belong to the Articulated series as a 

 primary subdivision of the Animal kingdom ; but they are the 

 most important, as enabling us most readily to distinguish its 

 members from all others. They will be dwelt upon in more 

 detail in their proper place. The animals composing the sub- 

 kingdom Mollusca are strikingly contrasted with them in a great 

 variety of particulars. In the first place, the body is soft, and 

 has no regularity of form. It may or may not be covered with 

 a shell ; but if this exists, it merely serves as a protection to the 

 body, and gives no assistance to its movements; no muscles 

 being attached to it, except such as connect the animal with the 

 shell, or the different pieces of the shell (where there are more 

 than one) to each other. In fact, the entire muscular system 

 consists of a few scattered bands and fibres, except in some of the 

 more active species, which partake of the characters of the Arti- 

 culata or Vertebrata. But, on the other hand, the organs of 

 nutrition attain a very high degree of development in this series ; 

 and the bulk of the body, which is often very considerable, is 

 given almost by them alone. We do not find in them any ten- 

 dency to symmetrical arrangement of any kind ; nor to a repe- 

 tition of parts, such as we have seen in the Badiata and Articu- 

 lata ; so that no definite form can be assigned as characteristic of 

 their fabric. An idea of the mode in which their organs are 

 arranged, in the lowest and simplest species, will be derived from 

 the examination of the accompanying figure, which represents 

 the anatomy of the Oyster. It will be seen that there is here an 

 absence of anything like a head; for the mouth, 5, is buried, as 

 it were, among the other organs, and cannot be projected from 

 between the valves ; and there are no other organs of sense, than 

 the tentacula or enlarged lips, #, that immediately surround it. 



