A FEW FACTS ABOUT ZOOLOGY. 



by a siphon that runs through the whole succession of cham- 

 bers. These chambered shells were once very abundant. 

 More than two thousand fossil species are known. They have 

 but one living representative — the pearly nautilus. This 

 straggler of a mighty race dwells at the bottom of the Indian 

 Ocean. The shell is well known, but only two or three 

 specimens of the animal have been obtained. Fig. 4 gives a 

 picture of a cuttle-fish. The squid and cuttle-fish have ten 

 arms, the additional pair being longer than the others. 



There are cuttle-fish and poulps (or devil-fish) so large as 

 even to be dangerous to a man who might be swimming near 

 them, and the stories of novelists, like Victor Hugo, have 

 some foundation in the large size and repulsive aspects of 

 these creatures. They crawl head downward, with their 

 arms on the bottom of the sea, and usually swim backward 

 or forward by means of fins, or squirt themselves backward 

 by forcing water through their funnels. 



We must carefully distinguish between affinity and anal- 

 ogy among animals. The former is founded upon identity 

 of plan; the latter upon external resemblance. At first sight 

 there may seem to be, in the cuttle-fish, with its circle of 

 arms, an analogy to the radiating type. In the radiates 

 every tentacle opens into one of the chambers, oris connected 



