93 



ZOOLOGY. 



Class III. — Ctenophora (Gomh-'bearers). 



General Characters of Ctenophores.— These beautiful an- 

 imals derive their name Ctenophora, 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 Adinozoa, 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 chymiferous 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 chymiferous tube, they 

 probably aid in respiration. These ani- 

 mals also stand much higher in the scale 

 of life than the other Coelenterates by 

 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 PleuroiracMa, from which, among 

 other nerves, eight principal ones are distributed to the 

 eight 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 



Fig. 61.— View of the 

 ^stro-vascular canals of a 

 Plmrohra^hia, f roniwhicti 

 tlie two retractile arms 

 have been removed. A, 

 from one side, the mouth- 

 opening above ; i?, eeen 

 from the mouth-end. — 

 After Gegenbaur, 



