ECHINOCYAMUS PUSILLUS. 



17 



Stadium with sixty segments. 



This cleavage stadium, which begins at about three hours after 

 the fecundation, is introduced b}^ the activity of the eight »large» macro- 

 meres, which become divided, apparently by a horizontal plane, in 

 sixteen equal segments arranged in two superposed rows. Then the 

 »small» macromeres begin to divide, the lowest ones at 'the vegetative 

 pole, as it seems to me, first taking part in the process. Lastly, the 

 four »lower» micromeres divide into eight. However, it is worthy of 

 notice that the succession of the segmentation phenomena in this sta- 

 dium is slightly variable. 



The difference in size between the blastomeres is still discernible, 

 though of course not so obvious; meanwhile the micromeres are still 

 minute, PL II, fig. 30. During repeated divisions, however, the diffe- 

 rence in size gradually becomes indistinguishable. 



The following table will give a view of the segmentation process 

 in Echinocyamus. 



By way of a brief recapitulation of what has been said in the 

 preceding pages with regard to the process of segmentation in Echi- 

 nocyamus, I may call attention to the following results: 



Nova Acta Reg. Soc. Sc. Dps. Ser. III. 



