ZOOLOGY. 



CLASS III. CTENOPHORA (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 



Fig. 61. -view of the len g th with a chymiferous tube, they 

 gastro-vascniarcanaisofa probably aid in respiration. These ani- 



Pleuroorachia, from which ,, n i i i 



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



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



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



opening above ; B, seen ITI-IJ. ixi TI 



from the 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 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 (lithocyst) seated upon the ganglion. 

 Eimer has lately shown that the nervous system of the 



