232 



PHYSICAL BASIS OF HEREDITY 



reciprocal showed neither a great predominance of the 

 characters of the paternal race, nor of the maternal race, 

 but rather certain characteristic features of purpuratus 

 and others of Franciscanns. The larval characters 

 appeared to be dominant or recessive taken singly. Until 

 an F2 generation can be raised it is obviously hazardous 

 to speak here of Mendelian dominance and recessiveness 

 of characters that are based on F^ observations alone, 

 especially since it is becoming more and more apparent 

 that many F, characters are more or less intermediate, 

 and there are no general grounds for expecting pure domi- 

 nance or recessiveness. 



Many crosses have been made between different species 

 of fish, and in some of these the young, at the time of hatch- 

 ing, are maternal. It has generally been supposed that 

 such cases are due to the absorption of the paternal chro- 

 mosomes at the first or at later cleavage stages. Loss of 

 chromosomes has in fact been recorded in several of these 

 cases of maternal inheritance. On the other hand, Miss 

 Pinney's observations, summarized in the following table. 



Cross Development Results Chromosomal Behavior 



Ctenolabrus 9 X Fundulus cf" Development cases Early mitotic behavior 



during gastrulation. is prevailingly nor- 

 mal. 

 Ctenolabrus 9 X Stenoto- 



mus o^ Many hatching em- Early mitoses are nor- 



bryos of the mater- mal. 

 nal type. 

 Ctenolabrus 9 X Menidia cf" Advanced development. Early mitoses are nor- 

 mal. 

 Ctenolabrus cf X Fundulus 9 One hatching embryo 



reported. Many ad- 

 vanced embryos — 

 maternal type. 

 Ctenolabrus cf X Stenoto- 



mus ^ Development ceases 



during gastrulation. 

 Ctenolabrus o' X Menidia 9 Two hatching embryos 



reported. Maternal 

 type. 



show that the maternal type may appear not only when the 

 early mitoses are abnormal, but in one case at least when 

 they are normal. It is quite possible, therefore, that while 



Abnormal nuclear be- 

 havior occurs. 



Abnormal mitosis pre- 

 dominant. 



Abnormal mitosis is of 

 frequent occurrence. 



