DEVELOPMENT OF THE OPOSSUM 41 



whole matter may be summarized by the statement that cleavage 

 proceeds in the opossum from the 1-celled to the IG-celled stage 

 superficially somewhat as in the Eutheria and without evident 

 polar differentiation, but that potentially the cells at the poles 

 differ, those of one hemisphere being destined to become the 

 formative, those of the other the non-formative region of the 

 early blastocyst. 



