98 DIFFERENTIATION III 



heterogeneous hybrids is due to the inability of the male 

 chromosomes to exert their activity in a cytoplasm to which 

 they are not adapted, or to the fact that such characters as 

 appear are not carried by the chromosomes at all. If the 

 latter were true then it might be supposed since the germ- 

 cells of the two sexes each carry a complete set of the 

 necessary specific chromosomes that some at least of the 

 characters of the larvae were not carried by the female 

 chromosomes either, but simply by the cytoplasm, a supposi- 

 tion which is certainly strengthened by the appearance of 

 certain Echinoid characters the primary mesenchyme, and 

 the inclination of the archenteron to the oral side in the 

 gastrulae reared from enucleate Sea-urchin egg-fragments ferti- 

 lized with Antedon sperm. In addition to this there is the 

 evidence from the defective development of ova from which 

 certain parts of the cytoplasm have been removed. 



While therefore we know that the determinants for some 

 characters reside in the cytoplasm, the results of heterogeneous 

 hybridization certainly suggest that these characters are the 

 large ones, those that put the organism in its phylum, class, 

 order, and family, the characters that make it an Echinoderm 

 and not a Worm or Mollusc, a Sea-urchin and not a Starfish 

 or a Feather-star, while the smaller characters, generic, specific, 

 individual are transmitted by the nucleus. The former are 

 perpetuated therefore by the female parent alone, the latter 

 equally by both parents. 



In the last resort, as we know, the cytoplasm is indebted to 

 the nucleus for several contributions to its structure the 'yolk- 

 nucleus ' and the contents of the germinal vesicle at matura- 

 tion but these are processes which find no counterpart 

 during the formation of the male cells, except perhaps in the 

 seemingly insignificant chromatoid accessory bodies. 



It has been suggested (by Driesch) that the characters 

 handed on through the cytoplasm are those that appear early 

 in development, while those that arise later are carried by 

 the nuclei. This is probably in the main true, as we have 

 known, since von Baer taught us, that the general appears 

 before the particular ( aus dem allgemeineren Typus bildet 



