CLASSIFICATION OF ANIMALS. tg 
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 Articuwlates. 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 
é gir this go to the eyes and the other 
Fig. 8.—Nervous System of an 
Insect. organs of sense. 
