ON THE ANIMAL KINGDOM. 201 



external or internal, the muscles being attached solely to 

 the skin, which is itself in general soft, though often pro- 

 tected by a calcareous or stony crust, termed the shell. 

 These animals, remarkable like plants for the variety of 

 modes in which the sexes are combined, have their nervous 

 system composed of several scattered masses or ganglions 

 united together by nervous threads. They are called 

 MoLLUSCA, and are almost all aquatic. 



A fourth form of animals presents to our view the or- 

 gans of locomotion and sense arranged in a circular dispo- 

 sition round a centre, so as to give a sort of radiant appear- 

 ance to the whole body. Their substance is more or less 

 gelatinous Avith the fibres indistinct. The nervous system 

 of these imperfect beings is but little known as yet; though 

 M. Tiedemann in his Memoire sur rAnatomie des AslerieSy 

 which was crowned by tlie French Institute, conceives 

 that the whitish threads which proceed in a ladiant di- 

 rection from around the mouth, and which extend them- 

 selves through the whole length of the arms of these ani- 

 mals, form a sort of nervous system which from the pulpy 

 nature of the medullary matter seems to correspond with 

 the gelatinous composition of the animals themselves. 

 They are all aquatic, and are named Radiata. 



There still remains a fifth form of animals to be consi-' 

 dered — beings which cannot in the present state of know- 

 ledge be better described than as masses of a transparent 

 homogeneous, mobile, and sensible pulp. There are how- 

 ever to be observed in this transparent pulp innumerable 

 minute granulations, which may be considered as the ner-> 

 vous molecules dispersed over, or as it were confounded 

 with, the substance of these animals, so as to impregnate 

 the whole with sensibility. 



