8o 



SYSTEMATIC ZOOLOGY 



long in proportion to the diameter of the bell ; a medusa thirty 

 centimeters in diameter may have tentacles a meter or more in 

 length, while in the largest species the} - are said to attain a 

 length of forty meters. Both the tentacles and the germ-glands 

 are often very brilliantly and beautifully colored ; the rest of the 

 animal is usually nearly colorless, and some are phosphorescent. 



y? n 





FlG. 67. Avrelia aurita. Oral aspect; two of the oral tentacles removed. a.r.c, radial 

 canal; gon, gonads or germ-glands ,.//>, marginal lappet; 



mouth; or.a, oral arm or tentacle; p.r.c, radial canal; s.g.p, subgeniial pit; /.tentacles. 

 (After Parker and Haswell.) 



CLASS III. CTENOPHORA 



The Ctenophora (Gr. tcrek, a comb, and (fropos, bearing) are 

 all marine, jellylike animals, and more colorless and transparent 

 than the other Cnidaria. They are sometimes called sea walnuts 

 because of the ovoid shape of the body of some species ; but some 

 are bandlike, and others saclike ( Tigs. 69, ;o. and 72 >. There is 

 a more or less radial arrangement of the parts, but as in the 



