126 N. YATSU. 



are comparatively normal, the gut is quite abnormal, the stomach 

 being larger than the oesophagus, and the position of the mouth 

 deviating from the normal. Nevertheless each part is complete, 

 except the apical organ. It should not be overlooked that the 

 apical organ is abnormal in every one of five defective pilidia, 

 while both the gut and ciliated lobes are fairly unaffected by the 

 operation. From this it is probable that the basis of the apical 

 organ is vaguely foreshadowed as early as the stage at which 

 the crerminal vesicle is still intact. 



o 



It is highly important to note that the formation of a pilidium 

 does not depend on the size of the piece, since one fourth of the 

 perfect larvae are decidedly smaller than the rest. The larva, lA, 

 is one of the larger group, and iB one of the smaller. Both are 

 perfect in every respect, but one is a little larger than one half of 

 the other. From the fact that, in spite of cutting the eggs at 

 random, a large percentage of perfect larvae were produced, that 

 the perfect ones vary greatly in size, and that the defects are not 

 so considerable as at a later period, the most natural interpreta- 

 tion one can draw would be that, antecedent to the dissolution of 

 the germinal vesicle, the egg cytoplasm still shows little or no 

 definite specification of the germ regions. 



SERIES B. 



Development of Fragments obtained at the MetapJiase of the first 



Polar Mitosis. 



The eggs were cut when the mitotic figure of the first matura- 

 tion division was completed ; this can readily be seen as a clear 

 space at the animal pole. The nucleated fragment was fertilized. 

 Sixty-five eggs thus operated were able to develop into larvae. 

 Owing to a change of consistency of either the gelatinous egg 

 envelope or the egg itself, I found it more difficult to operate at 

 this stage than at any other. The result was : 



Perfect pilidia 34 52.3 per cent. 



Defective pilidia 31 47.7 per cent. 



Notwithstanding the difficulty of the operation, it was compara- 

 tively easy to cut off a considerable part of cytoplasm from the 

 egg of this stage on account of the peripheral position of the 



