CTENOPIIOKA. 



71- 



the stage with four segments, the segments are so disposed that two 

 perpendicular planes placed between them would correspond to the 

 two principal planes of the fully developed animal. Each of the four 

 spheres gives rise to one of the four quadrants of the' adult animal 

 (Fol.) The whole mass of the finely granular exoplasm now becomes 

 collected at the upper end of the segmentation spheres, where it is 

 separated off and gives rise to eight new small spheres. These, by 

 continued division, break up into a great number of small nucleated 

 cells, which increase rapidly and grow round the eight large seg- 

 mentation spheres or the cells produced from them. 



The young Ctenopliora sooner or later leave the egg membranes, 

 and at this period differ more or less from 

 the sexually mature animal in the simpler 

 and usually more spherical form of the 

 body, in the small size of the tentacles 

 and swimming plates, and in the differ- 

 ence in the relative size of the O3sophageal 

 tube, infundibulum, and vascular canals. 

 The differences are most striking in the 

 lobed Ctenophora (with the exception of 

 Cestum), the embryos of which have a 

 great similarity to the young of Cydippe, 

 and have no traces of bi-radial structure. 

 It is only after a longer period of larval 

 life that the completely mature form is 

 attained by the unequal growth of the 

 swimming plates and their canals, the out- 

 growth of the tentacle-like processes, and 

 the formation of two lobe-like projections 

 round the mouth from those halves of the 

 body which correspond to the longer rows 

 of swimming plates. The phenomenon 



remarked by Chun is worthy of notice, that the young of Eucharis, 

 while still in the larval stage, become sexually mature during the 

 hot period of the year. 



The Ctenophora live in the warmer seas, and, under favourable 

 conditions, often appear in great quantities at the surface. They 

 feed on marine animals of various size, which they capture with 

 their tentacles. Many, as the Beroidce, which do not possess tenta- 

 cles, are compensated for this deficiency by the possession of an 

 unusually large mouth (fig. 205), by means of which they are able 



FIG. 2<lo. Beroe ovatus. Of, 

 Lithocyst, at its sides are the 

 small tentacles of the polar 

 areas ; Tr, infundibulum. 



