Evidence from Somatic Histogenesis 43 



Conklin has expressed more definitely than any other biol- 

 ogist with whose writings I am acquainted, the idea men- 

 tioned above, that cytoplasm "influences" heredity in early 

 ontogenetic stages, and also influences adult attributes of 

 the major taxonomic groups, but becomes inoperative in 

 the later stages of development, the heredity of these being 

 transferred to the nucleus. He says, "In short, the egg 

 cytoplasm fixes the general type of development and the 

 sperm and egg nuclei supply only the details." And fur- 

 ther: "We are vertebrates because our mothers were 

 vertebrates and produced eggs of the vertebrate pattern ; 

 but the color of our skin and hair and eyes, our sex, stature, 

 and mental peculiarities were determined by the sperm as 

 well as by the egg from which we came. There is evidence 

 that the chromosomes of the egg and sperm are the seat of 

 the differential factors or determiners for Mendelian char- 

 acters, while the general polarity, S} T mmetry, and pattern 

 of the embryo are determined by the cytoplasm of the 

 egg." If two points in this last quotation be viewed in 

 the light of a large mass of relevant evidence not usually 

 taken into account in recent discussions on heredity, and 

 if strict consistency in the use of terms be maintained, the 

 general conclusion will be quite different from that stated 

 by Conklin. These two points, the conception of "differen- 

 tial" and of "determiner," must now receive attention ; but 

 first I will illustrate my position by a case presenting the 

 kind of evidence to which I have referred. 



Species Attributes in Single Cells of Adult Organisms 



In general, this evidence comes from the field of histology, 

 or more strictly histogenesis. The most convincing, because 

 the most direct, evidence from this source is that pertaining 

 to the development of hereditary structures in adult meta- 

 zoa and metaphyta. The structures in such organisms 



