304 



GENERAL EMBRYOLOGY 



(Godlewski, Baltzer) while the larvae resulting from this cross 

 exhibited certain characters which were purely maternal; but 

 this result is wholly inconclusive as evidence opposing the hy- 

 pothesis of nuclear control. 



FIG. 141. History of the paternal chromatin in the pseudohybrids of the sea- 

 urchins, Strongylocentrotus 9 X Sphcerechinus 6\ After Baltzer. A. Cleavage 

 cell showing paternal chromatin (c?) outside the division figure. B. Early 

 blastula. C. Late blastula, showing the elimination of the paternal chromatin 

 in the irregular cells and spaces within the blastoccel (for normal blastula see 

 Fig. 109). 



For it has been found, in the first place, that external condi- 

 tions often determine whether certain characters shall be 

 paternal or maternal in their qualities (Vernon, Tennent). 

 Under certain conditions of temperature, alkalinity, etc., the 

 larva may exhibit paternal resemblances, while under other 

 conditions maternal resemblances may appear in the same 



