Prolegomena 195 



by proper embryological and genetic experimentation. We may reserve 

 the term "cytoplasmic specificity" for the genuine specificity by cyto- 

 plasmic continuity with the ancestors, and designate the specificities 

 produced in the egg under genie control as "predetermination," a term 

 in use in experimental embryology, or, as I proposed ( Goldschmidt, 

 1951fl), as "conditioning of the cytoplasm." The latter phenomenon 

 must show what Toyama ( 1913 ) called, rather unfortunately, "mater- 

 nal inheritance," while the former will show real matroclinous heredity. 



There is a condition intermediate between these two types of 

 cytoplasmic specificity, a cytoplasmic condition of specific nature 

 which is not continuous with the ancestral cytoplasm but is induced 

 at a definite moment by external means, experimentally. Such a condi- 

 tion has been called Dauermodifikation (Jollos, 1913, 1921). Theoreti- 

 cally, it might result in a lasting change into a new specificity; or it 

 might be diluted in subsequent cell divisions and fade out completely. 



Of the three groups of cytoplasmic specificity thus far delineated 

 — specificity through ancestral continuity, through genie conditioning 

 in the egg stage, and through experimental change — only the first may 

 properly be called a type of cytoplasmic heredity. It is characterized 

 as a generalized biochemical and antigenic condition of the cytoplasm 

 as a substrate. This would, therefore, become recognized in genetic 

 experiments, when a shift of genically controlled reactions takes place 

 according to the type of cytoplasm present (usually in reciprocal 

 crosses or in nuclear transplantation ) . It cannot be expected that such 

 a cytoplasmic efFect of a specific substrate could be distinguished in 

 all or even in many of the developmental effects under nuclear control 

 (i.e., Mendelizing traits). Whatever that specificity means biochemi- 

 cally (e.g., serological specificity), it may be assumed that such effects 

 of different cytoplasmic specificity would be shown only in Men- 

 delizing traits that are capable of small but recognizable quantitative 

 variations. The reason for this expectation is that in genetic experi- 

 mentation only nearly related forms may be successfully crossed and 

 bred to further generations. Cytoplasmic differences of such an order 

 that developmental processes would be changed qualitatively ac- 

 cording to the cytoplasm present would be expected only in crosses 

 between species and still higher categories. But they might be recog- 

 nizable in experiments with merogony and nuclear transplantation. 



At this level of what in its entirety is called cytoplasmic in- 

 heritance, another problem enters. As a rule we think only of 

 inheritance within the cytoplasm of the egg; and, therefore, all tests 

 for cytoplasmic inheritance are based upon reciprocal crosses. The 



