A FEW FACTS ABOUT ZOOLOGY. 



with a radiating tube, or, as in the star-fishes, with a loco- 

 motive sucker; whereas, in the cuttle-fish the feelers are only- 

 external appendages, in no way connected with the essential 

 structural element. We have a striking illustration of this 

 superficial resemblance in the wings of birds and insects. 

 In birds, wings are a typical feature, being attached and 

 forming a part of the internal skeleton; the wing in an in- 

 sect, on the contrary, is a flattened, dried-up gill, not being 

 built at all on the same plan. We associate them together 

 merely because each is used for flying. 



Having now made a hasty survey of two of Cuvier's divis- 

 ions, the radiates and the mollusks, we come to 



The Articulates. 



Here we have again three classes — worms, crustaceans, 

 and insects. The lowest of these three classes, the worms, 

 shows us the typical structure with little division into parts. 

 The body is a long cylinder, divided through its whole 

 length by movable joints ; the nervous force is scattered 

 throughout the whole body; if cut in two the front part may 

 build up for itself a new tail, while the hind part produces a 

 new head, and both continue to live as new animals. The 

 ease with which the animal sustains injuries does not arise 

 from its intense nervous force, but from the fact that the 

 nervous force is scattered, and not concentrated at any one 

 point. A serious injury to the brain of a backboned animal 

 would kill it at once, for the brain contains the very essence 

 of its life. 



The articulata are the jointed animals. We have already 

 spoken of the worm's body as being formed of a succession 

 of rings or movab'e joints; this structure is found in earth- 

 worms, and in the worms that live on other bodies as para- 

 sites, as the tape-worm. Among the articulata we place 

 lobsters and crabs. It may seem at sight that nothing can 

 be more unlike a worm than a lobster; but comparison shows 



