92 



ZOOLOGY. 



CLASS III. CTEISTOPHOKA (Comb -bearers). 



General Characters of Ctenophores. These beautiful an- 

 imals derive their name Ctenopliora, 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 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 



. . , mi 



gastro-vascniar canals of a probably aid in respiration. Inese ani- 



Pleurobrachia, from which -, -, i i i j_i i 



the two retractile arms mals also stand much higher in the scale 

 f rom onTside^he 'mouth- of life than the other Coelenterates by 

 fTm in ?he b mo e u ; th 7 cnr- being more truly bilateral, the radial 

 After Gegenbaur. 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 Pleurobrachia, 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 (litkocyst) seated upon the ganglion. 

 Eimer has lately shown that the nervous system of the 



Fig. 61. View of the 



