CCELENTERATA : CTENOPHORA. 177 



"apical," and the rest of the body constitutes the interpolar 

 region. At the oral pole is the transverse mouth, bounded 

 by lateral, slightly protuberant margins. " Eight meridional 

 bands, or 'ctenophores' bearing the comb -like fringes, or 

 characteristic organs of locomotion, traverse at definite in- 

 tervals the interpolar region, which they divide into an equal 

 number of lune-like lobes, termed the 'actinomeres;' but 

 this division of the body does not extend into the immediate 

 vicinity of the poles, before reaching which the ctenophores 

 gradually diminish in diameter, each terminating in a point " 

 (Greene). The normal number of the ctenophores is eight 

 (four or twelve in some other forms), and each consists of 

 a band of surface elevated transversely into a number of 

 ridges, to each of which a fringe of cilia is attached, so as to 

 form a comb-like plate. The cilia in the middle of these 

 paddle-like transverse ridges are the longest, and they gradually 

 diminish in length towards the sides, so that the form of each 

 comb is somewhat crescentic. Beside the comb-like groups 

 of vibratile cilia, Pleurobrachia is provided with two very long 

 and flexible tentacular processes, which are fringed on one 

 side with small cirrhi. These filamentous processes arise 

 each from a sac, situated on one of the lateral actinomeres, 

 within which they can be completely and instantaneously re- 

 tracted at the will of the animal. 



The mouth of Pleurobrachia (fig. 90, a) opens into a 

 fusiform, digestive sac, or stomach (b\ the lower part of which 

 is provided with brown cells, supposed to discharge the func- 

 tions of a liver. The stomach opens below into a shorter and 

 wider cavity (c\ termed the "funnel," from which two canals 

 diverge in the direction of the vertical axis of the organism, to 

 open at the "apical pole." These canals are known as the 

 "apical canals" (e), and their apertures as the "apical pores." 

 From the funnel two other pairs of canals are given off. Of 

 these, one pair known as the "paragastric canals" turns 

 upwards, one running parallel to the digestive sac on each side 

 (*/), and "terminating csecally before quite reaching the oral 

 extremity." The second pair of canals (i) the so-called 

 "radial canals" branch off from the funnel laterally, each 

 dividing into two, and then again into two, as they proceed 

 towards the periphery of the body. Thus the two " primary " 

 radial canals produce four "secondary" canals (), and these, 

 in turn, give rise to eight "tertiary" radial canals (/), which 

 finally terminate by opening "at right angles into an equal 

 number of longitudinal vessels, the ' ctenophoral ' canals (/), 

 whose course coincides with that of the eight locomotive 



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