INVERTEBRATE ANIMALS, 



MOLLUSCS. 



We now come to the second great division into which all animated 

 beings have been distinguished. All the creatures which we have hith- 

 erto examined, however different in form they may be, the ape and the 

 eel being good examples of this external dissimilarity, yet agree in one 

 point — namely, that they possess a spinal cord protected by vertebrae, 

 and are therefore termed vertebrated animals. 



But with the fishes ends the division of vertebrates, and we now enter 

 upon another vast division, in which there are no true brain and no ver- 

 tebra. These creatures are classed together under the name of inver- 

 tebrate animals — a somewhat insufficient title, as it is based on a nega- 

 tive, and not on a positive, principle. Whatever may be its defects, it 

 has been too long received, and is too generally accepted, to be dis- 

 turbed by a new phraseology ; and, though it be founded on the ab- 

 sence, and not on the presence, of certain structures, it is concise and 

 intelligible. 



The first order of invertebrate animals is called Mollusca — a name 

 given to these creatures on account of the soft envelope which surrounds 

 their bodies. 



The highest of the Molluscs are those beings which are classed to- 

 gether under the title of Cephalopoda. This term is derived from 

 two Greek words, the former signifying " a head," and the latter " a 

 foot," and is applied to these creatures because the feet — or arms, as 

 they might also be called — are arranged in a circular manner round 

 the mouth. 



They are all animals of prey, and are furnished with a tremendous 

 apparatus for seizure and destruction. Their long arms are furnished 

 with round hollow discs set in rows, each disc being a powerful sucker, 

 and when applied to any object retaining its hold with wonderful te- 

 nacity. The mode by which the needful vacuum is made is simple in 

 the extreme. The centre of the disc is filled with a soft, fleshy protu- 

 b'erance, which can be withdrawn at the pleasure of the owner. When, 

 therefore, the edges of the disc are applied to an object, and the piston- 

 like centre withdrawn, a partial vacuum is formed, and the disc adheres 

 like a cupping-glass or a boy's leather sucker. 



These discs are all under the command of the owner, which can seize 

 any object with an instantaneous grasp, and relax its hold with equal 

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