20 



NATUKAL HISTOKY. 



16. The third division of the animal kingdom is that 

 of the Mollusks. This term comes from the Latin word 

 mollis, soft. Mollusks are soft animals, most of them 

 being inclosed in a hard shell, as the oyster, and all the 

 varieties of shell-fish; and others being naked, as the 

 slug. The central organs of the nervous system are 

 ganglia variously arranged in the different orders of 

 these animals. 



17. The fourth sub-kingdom of animals is that of the 

 Radiates. In Fig. 9 you have a representation of one 



Fig. 9. Star-fish. 



of tnese animals, the star-fish, which will show you why 

 they are called Radiates. You see parts extending like 

 rays from the central portion. Radius is the Latin 

 word for ray, and hence the name Radiate. 



18. It is the upper side of the star-fish that you see in 

 this figure. On the under side it has a mouth in the 

 centre. The arrangement of its nervous system is sin- 



