CLASSIFICATION OF ANIMALS. 341 



IV. Jugulares ; ventral fins in the front of the thoracic. 



1 Gadus, hadock, cod, whit- 3 Blennius, blenny 



ing, ling 4 Callionymus, dragonet 



2 Uranoscopus, stargazer 5 Trachinus, weaver 



The animals which have no vertebral column do not possess so 

 many common characters as the vertebral classes. Their hard parts, 

 when they have any, are generally placed on the surface of the body. 

 The centre of the nervous system, instead of being inclosed in a 

 bony case, lies in the same cavity with the viscera. The oesophagus 

 is generally surrounded by a nervous chord coming from tiie brain. 

 Their respiration is not carried on by lungs ; and they have no 

 voice. Their jaws move in various directions. They have no uri- 

 nary secretion. 



The invertebral animals were distributed by Linnaeus into two 

 classes; insects and worms, (vermes). The anatomical structure of 

 these animals was very imperfectly known, when the Swedish natu- 

 ralist first promulgated his arrangement. But the labours of sub- 

 sequent * oh gists, and particularly those of Cuvier, have succeeded 

 in esrufiis'iiug such striking and important differences in their forma- 

 tion, Jhat a subdivision of the Linuaean classes became indispensably 

 necessary. The insects of Linnaeus are divided into crustacea and 

 iusecta : and the vermes of the same author form three classes; viz* 

 raoliusca, vermes, and zoophyta. 



Tiie mollusca derive their name from the soft fleshy nature of 

 their body. This class includes those pulpy animals, which may 

 either be destitute of an external covering, when they are called 

 moilusca nuda, as the slug ; or may be enclosed in one or more 

 shells, as the snail, oyster, &c. when they are termed testacea. 



The animals of this class have no articulated members ; they have 

 blood-vessels, and a true circulation. They respire by means of 

 giils. They have a distinct brain, giving origin to nerves ; and a 

 spinal marrow. 



1 Sepia, cuttle-fish 7 Clyo 



2 Argonauta 8 Patella, limpet 



3 Nautilus 9 Helix, snail 



4 Limax, slug 10 Haliotis, Venus's ear 



5 Aplysia 1 1 Murex, caltrop, or rock.shell 



6 Doris 12 Strom bus, screw 



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