ACTINOZOA. 143 



as a typical example of the group, should in this 

 place be given {fig. 39, e). 



The body, or * actinosome,' of Pleurobrachia is 

 sub-spherical or melon-shaped, colourless, gela- 

 tinous, and perfectly transparent, but displaying, 

 in sunlight, tints of a beautiful iridescence. 



Two poles, an oral and an apical, mark the 

 opposite extremities of the axis of the animal. 

 The slightly protuberant mouth appears, when 

 closed, as an elliptical fissure, presenting two 

 flattened sides and two opposing edges. 



Eight meridional bands, or ' ctenophores,' bear- 

 ing the comb-like fringes, or characteristic organs 

 of locomotion, traverse, at definite intervals, the 

 interpolar region, which they divide into an equal 

 number of lune-like lobes, termed the 'actino- 

 meres.' 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. 

 Around the apical pole, in particular, may be 

 noticed a somewhat oblong, depressed, area, dis- 

 tinctly circumscribed by the adjacent converging 

 actinomeres. 



The eight actinomeres are by no means 

 equal in size, and, to understand their relations 

 aright, it seems desirable to distinguish three 

 principal kinds of these parts as the antero- 

 posterior, the lateral, and the accessory actino- 

 meres. 



The two antero-posterior actinomeres, wider than 

 their fellows, are opposite to each other and the 

 edges of the elliptical mouth. At right angles to 

 these, but in like manner opposite one another, 

 lie the two lateral actinomeres, which, therefore. 



