CLASSIFICATION OF ANIMALS. 19 



a representation of the brain and spinal marrow of man, 

 with the beginnings of the nerves that branch out from 

 them. Essentially the same arrangement exists in all 

 the vertebrate animals. 



13. The second grand division or sub-kingdom of ani- 

 mals is that of the Articulates. They have a jointed or 

 articulated covering, as, for example, in the case of the 

 lobster. They have no skeleton inside, as the Verte- 

 brates have, but their coat of armor, as we may call it, 

 is their skeleton. The muscles are all fastened to this. 

 Thus, in the lobster, the muscles moving the claw have 

 one end attached to some portion of the shell of the body, 

 and the other to the shell of the claw. 



14. The chief classes or tribes of the Articulates are 

 the crab tribe, the worms, the spider and scorpion tribe, 

 and the insects. In the crab tribe the jointed covering 

 is very hard, being composed chiefly of a mineral sub- 

 stance the carbonate of lime. In most of the insects it 

 is very firm, and there is a marked resemblance in the 

 claws of such insects as beetles to those of crabs and 

 lobsters. Even in the worms the covering is firm com- 

 pared with the soft interior parts. 



15. The arrangement of the central organs of the nerv- 

 ous system of the Articulates is very different from that 



of the Vertebrates. There is no 

 skull with a brain in it, and there 

 is no spinal cord. There is a chain 

 of little brains, as we may say, con- 

 nected together by nerves, as rep- 

 resented in Fig. 8. Each of these 

 is called a ganglion (plural ganglia). 

 The first ganglion may be consid- 

 ered, for the most part, as corre- 

 sponding with the brain in the 

 Vertebrates, for the nerves from 

 this go to the eyes and the other 



Fig. 8. Nervous System of an 



insect. organs of sense. 



