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 hitherto 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 is no true brain and no vertebrae. These creatures are classed 

 together under the name of Invertebrated animals ; a somewhat insufficient title, as it is 

 based upon a negative and not on a positive principle. Whatever may be its defects, it 

 has been too long received, and is too generally accepted, to be disturbed by a new 

 phraseology, and though it be founded on the absence and not the presence of certain 

 structures, it is concise and intelligible. 



Numerous as are the species of the vertebrated animals, those of the invertebrates out- 

 number them as an army outnumbers a company. Although many species of mammals, 

 birds, reptiles, and fishes, are at present known to science, and the yet unrecognised species 

 are necessarily extremely numerous, there is some hope of obtaining an approximate 

 calculation of their respective numbers. But with the invertebrates, any approach to a 

 census even of known forms is well-nigh impracticable ; and as it is evident that the 

 ocean alone contains within its fathomless depths myriads of beings as yet hidden from 

 mortal eyes, the reader may conceive the utter impossibility of offering the slightest 

 conjecture respecting their numbers. 



It is evident, therefore, that in a work of this limited extent, no complete and detailed 

 history of the invertebrates can be attempted, and that the utmost that can be achieved is, 

 to give a general outline of each class and order, to describe and figure the leading or 

 typical forms, and to give occasional detailed accounts of certain species, selected for the 

 beauty or singularity of their form, for the interesting nature of their habits, or for their 

 direct usefulness to man. 



IN entering upon a wholly new class of beings, we are forced to abandon the charac- 

 teristics on which we lately depended for the classification, and to seek for new structures 

 whereon to build our system. The peculiar formations which are now accepted for this 

 purpose will be mentioned as we proceed with the work. 



THE first order of Invertebrated animals is called MOLLUSCA, a name given to these 

 creatures on account of the soft envelope which surrounds their bodies. . Most of the 

 Molluscs are farther protected by a larger or smaller shell, and in former days, when mere 

 externals were rated beyond their real value, with the great mass of naturalists, or rather of 

 virtuosi, the shell was the only portion of the animal that was considered, and the study of 

 these beings was therefore termed conchology, or " shell-lore." Beautiful as the shells 

 are, and capable as are the present school of naturalists of appreciating the gorgeous 

 richness or tender delicacy of their colours, and the strange eccentricity or exquisite grace 

 of their forms, those who study these beings have now learned to comprehend that the 

 shell is, despite of all its beauty, but a secondary consideration, and that the true naturalist 

 cares not so much for the lifeless shell as for the creature which inhabited it, and from 

 whose tissues it was formed. 



In the course of the few pages which can be given to the Molluscs, the reader will 

 observe that, wherever practicable, the form of the inhabitant has been given together with 

 that of the shell. There are, moreover, many most curious and interesting forms among 

 the Molluscs, where not a vestige of shell exists, and which, by the former plan, would be 

 entirely excluded from the attention of the " conchologist." 



Before proceeding to describe the different species of Molluscs, I will briefly recount 



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