IV. i INITIAL STRUCTURE OF THE GERM 



211 



the other half of the funnel (Fig. 119 u-y\ Fischel has carried the 

 analysis of the potentialities of the blastomeres a step further 

 (Fig-. 119 h-k). Though cleavage is partial, as described by 

 Driesch and Morgan, there are slight irregularities in the position 

 of the blastomeres. A |- blastomere produces one costa only, 

 ^g- blastomeres (four macro- and four micromeres) four costae, y 



, 



and 



T g, 



when 



(five macro- and five micromeres) five, 

 separated in the same way, respectively three, six, and two costae. 

 Similar results were obtained by meridional division of the egg 

 Fischel confirms the statements of the other 



in later stages. 



FIG. 120. a. Beroe ocata : egg in the 16-cell stage. The micromeres 

 disarranged by pressure ; b. The resulting larva with two sense-organs, 

 and four costae radiating from each : one stomodaeum. (After Fischel, 

 1898.) c. Normal segmentation of the egg of Berde from which a small 

 portion of the vegetative hemisphere has been removed ; d. Larva pro- 

 duced from the same, with eight costae, four endodermal canals, and 

 one (central) stomodaeum. (After Driesch and Morgan, 1896.) 



investigators as to the structure of the half larvae. In f larvae, 

 however, not three, but four, canals are formed, and the stom- 

 odaeum is vertical. The sense-organ is not found in embryos 

 developed from small fragments. Removal of the macromeres 

 left the number of costae unaffected, but displacement of the 

 micromeres by pressure led to the formation of an abnormal larva 

 with two sense-organs and eight costae arranged in two groups 

 of four each round each sense-organ (Fig. 120 a, V), or, if the 

 micromeres were separated into two lots, a group of four round one 

 organ, a group of three round the other, and some scattered combs. 

 With greater pressure three sense-organs were produced and the 



P a 



