6 The Ohio Journal of Science [Vol. XVII, No. 1,. 



transmitted by the cytoplasm of the egg alone. If the disease 

 is due to an infection to the germ of which chromatin has so far 

 proven immune, the transmission of variegation is no more 

 heredity, it seems to me, than is intrauterine transmission of 

 syphilis. But if by disease we mean merely a defect, then this 

 defect is found only in the cytoplasm. Perhaps the results can 

 be explained by assuming that the defect lies in the chromato- 

 phores themselves, that these are autonomous bodies arising 

 only from other bodies like themselves, and that they are 

 handed on to new generations only in the cytoplasm of the egg. 

 This is clearly not opposed to inheritance through the chromo- 

 somes as a general phenomenon. 



All the other phenomena listed above in support of cyto- 

 plasm as an agent in heredity involve only developmental 

 stages. Polarity directly traceable to polarity of the egg has 

 reference only to an early larval stage. The symmetry referred 

 to differences of the cytoplasm, applies only to the embryo. 

 The ascidians from which muscles or notochord were missing, 

 due to removal of part of the egg, were observed only in larval 

 stages. The matrocline hybrids among echinoderms have been 

 observed only as larvae. Unfortunately, it has been found 

 impracticable to rear them to the adult stage. No one knows 

 whether the reciprocal hybrids would or would not be dissimilar 

 as adults. 



In view of the fact that much of the evidence that the cyto- 

 plasm influences heredity comes from embryonic stages, may 

 we not harmonize the once conflicting views regarding chromo- 

 somes and cytoplasm in the following manner? Barring such 

 characters as variegation in Mirabilis, for which there is a 

 special explanation, it may be assumed that the cytoplasm often 

 (perhaps usually) determines the type of cleavage, the early 

 course of development, and in large measure the larval char- 

 acters, while the adult characteristics are determined by the 

 chromosomes. With the developmental stages the student of 

 heredity using the usual breeding methods has little to do. He 

 may be pardoned a bias in favor of the chromosomes because he 

 rarely studies larval characters. To the physiologist and mor- 

 phologist, on the other hand, the rigid conviction of the gene- 

 ticist that the chromosomes contain all the tools of his trade 

 has not unnaturally been viewed with skepticism. 



