93 ZOOLOGY. 



CLASS III. CTENOPHORA (Comb-bearers). 



General Characters of Ctenophores. These beautiful an- 

 imals derive their name Ctenophortt, or " comb-bearers," 

 from the vertical rows of comb-like paddles (ctenophores) 

 situated on meridional bands of muscles which serve as lo- 

 comotive organs, the body not contracting and dilating as 

 in the true jelly-fishes. In their organization they are 

 more complicated than the Actinozoa, as they have a true 

 digestive cavity passing through the body-cavity, with two 



posterior outlets (it will be remembered 

 that Cerianthus has one at the end of 

 the body). From this alimentary canal 

 are sent off chymifcrous or water-vascu- 

 lar canals (Fig. 61) which correspond in 

 their mode of origin with the water- 

 tubes of the Echinoderms. As regards 

 the rows of paddles, each vertical row 

 consists of a great number of isolated, 

 transverse, comb-like fringes placed one 

 above the other, and movable, either 

 isolately or in regular succession or 

 simultaneously (Agassiz). As these rows 

 of paddles are connected for their whole 

 length with a chvmiferous tube, they 



Fig. 61. View of the > . / 



gastro-vascuiar canals of a probably aid in respiration. Ihese ani- 



Pleurobrachia, from which . . . . , 



the two retractile arms mals also Stand nilicll higher 111 tllO SCale 



have been removed. A, -.. ., ,, ,, ,-, -, 



from one side, the mouth- of life than the other Coelenterates by 



opening above ; B, seen i i i i , ixn 1-1 



from 7he mouth-end. being more truly bilateral, the radial 



symmetry so marked in the Actinia or 

 in the jelly-fish being in these animals less apparent, as the 

 parts are developed on opposite sides of a median plane. 

 The nervous system, as originally described by Grant, con- 

 sists of a ganglion situated at the aboral end (end opposite 

 to the mouth) of the PleurobracJiia, from which, among 

 other nerves, eight principal ones are distributed to the 

 eighf rows of paddles. A nerve also proceeds to the so- 

 called otolitic sac (lithocyst) seated upon the ganglion. 

 Eimer has lately shown that the nervous system of the 



