CTENOPHORA. 



205 



network (wandering cells) of the jelly. The mouth is a new formation, and 

 the stomodaeum (stomach) arises as an invagination of ectoderm at the lower 

 pole (Fig. 163, 7, 8, 9}. y 



The larva when hatched differs more or less from the sexually mature arfiimal 

 in the simpler and usually more spherical form of the body, in the small size of 



FIG. 163. Development of Callianira Ualata (after Metschnikoff). 1, stage with eight ; 3, stage 

 with sixteen blastomeres ; 3, the eight upper cells of the previous stage have divided into 48 

 micromeres (ectoderm), which form a cap on the 8 macromeres (endoderm) ; &, side view of an 

 older stage ; 5, embryo in the stage of formation and invagination of mesoderm (Ms) ; 6, more 

 advanced stage in sagittal section ; 7, stage with developing stomodaeum ; 8, later stage with 

 commencing formation of tentacles ; 9, ripe embryo ; T tentacles ; Ot sense-organ ; mouth ; 

 Me mesoderm (jelly). 



the tentacles and swimming plates, and in the difference in the relative size of the 

 oesophageal tube, infundibulum, and vascular canals. The differences, putting 

 Cestus on one side, are most striking in the lobed Ctenopliora, the embryos of 

 which have a great similarity to the young of Cydippe. It is only after a longer 



