Nov., 19 IG] Cytoplasm and Heredity 7 



I claim no originality for the above attempt at harmony. 

 The idea I have expressed was first propounded, I beheve, by 

 ConkHn in 1908. I am, however, able to advance in favor of 

 Conklin's view evidence which was not available when Conklin 

 wrote. In my own work on rotifers I have discovered a case of 

 matrocline hybrids which, unlike those of the echinoderms, 

 were easily reared to the adult stage, at which time they were 

 wholly alike. The facts of this case are as follows: The rotifers 

 are one of the groups of animals that lay both parthenogenetic 

 and sexual eggs. The former hatch regularly in 14 to 18 hours 

 after laying, the latter remain in the egg a week or longer. 

 Moreover, whereas all the parthenogenetic eggs usually hatch, 

 only a fraction of the young developed in sexual eggs ever 

 emerge. The proportion of sexual eggs hatching varies greatly 

 in different lines. In line A, in the experiments above referred 

 to, about fifty per cent of the sexual eggs hatched. They began 

 to hatch about a week after they were laid, and two weeks later 

 practically all had hatched that would hatch at all. The time 

 spent in the egg was thus fairly uniform. Line B was strongly 

 contrasted with line A both in the total number of sexual eggs 

 that hatched and in the length of time spent in the egg. Only 

 five per cent of the eggs of line B ever hatched. Morover, their 

 hatching was spread irregularly over a period of five or six weeks. 



The reciprocal hybrids obtained from crosses between these 

 two lines were very unequal. When line A furnished the mother, 

 line B the father, the eggs laid by the females hatched in one to 

 three weeks, like line A, and about fifty per cent of them 

 hatched, also like line A. When line B furnished the mother, 

 the hatching of the eggs occupied four or five weeks, and the 

 total number hatching was about thirty per cent. In both 

 respects the hybrid eggs in this cross were intermediate between 

 the parent eggs. 



Here the reciprocal hybrids are very unlike, each being much 

 nearer the maternal condition. But when new lines were 

 obtained from these hybrid eggs, and these lines produced 

 sexual eggs of their own, the two reciprocal hybrid lines were 

 fully equal. Doubtless the inequality of the reciprocal hybrid 

 eggs was due to the cytoplasm furnished by the mother; but 

 when adults were developed from these eggs, and new cytoplasm 

 was produced under the influence of the paternal as well as the 



