27G ZOOLOGT 



certain number of canals run out along the surface of the jelly- 

 like body. The surface of the body is clad with special hair- 

 like Ijodies or cilia, which are arranged after the manner of 

 the teeth on a comb. A large number of combs is placed in 

 each of the rows running from the upper to the lower pole, and 

 by their incessant beating the animal is driven forward. 



The body of the ctenophore is very transparent, a result of 

 its composition ; for it is made up chiefly of water with a small 



Fig. 266. — Aitianijin dnnw, a cluster of our Northern roral-polyps, resting 

 on limy bases of their own secretion. The animals arc extremely delicate 

 and transparent. From a lithograph by Louis Agassiz's artist Sonrel. 



amount of pure jelly. Consequently the organism is as clear 

 as the sea itself, so that the animal is hard to distinguish. 

 Manjr marine animals are as transparent as the water, and there 

 is reason for thinking that the^^ enjoy, in consequence, a certain 

 immunity from attack by their enemies. It is curious, how- 

 ever, that these same animals are phosphorescent, so that they 

 glow brilliantly in the water at night, especially after irrita- 

 tion (Fig. 267). 



Coral reefs are almost exclusively the product of coral 

 poh-jis modified by the environmental conditions. The reef- 

 building corals live in shallow water from low-water mark to 

 a depth of one hundred feet only. Their distribution along 



