MOLLUSCS. 35S 



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 vertebras. 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 

 outnumber them as an army outnumbers a company. Although many species of mam- 

 mals, birds, reptiles, and fishes, are at present known to science, and the yet unrecog- 

 nized 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 struct- 

 ures 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 colors, and the strange eccentricity or ex- 

 quisite grace of their forms, those who study these beings have now learned to compre- 

 hend 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 in- 

 habited 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." 



