CCELENTERATA I ACTINOZOA. 143 



two poles of the sphere are termed respectively the " oral " and 

 " 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 appears 

 to be eight, and each consists of a band of surface elevated 

 transversely into a number of ridges, to each of which a fringe 



Fig. 52. Ctenophora. Pleurobrach ia pileiis. 



of cilia is attached, so as to form a comb-like plate. The 

 cilia in the middle of these 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 pro- 

 vided with two very long and flexible tentacular processes, 

 which are fringed on one side with smaller cirrhi. These 

 filamentous processes arise each from a sac, situated on one of 

 the lateral actinomeres, within which they can be completely 

 and instantaneously retracted at the will of the animal. 



The mouth of Pleurobrachia (fig. 53, a) opens into a 

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

 is provided with brown cells, supposed to discharge the 

 functions of a liver. The stomach opens below into a shorter 



