3 i8 



THE QUARTERLY REVIEW OF BIOLOGY 



which are indeed a restatement of the 

 present writer's ('17, '2.0b, etc.) views 

 (unknown to the author), e.g. "It is a 

 tenable hypothesis that this is the way 

 in which all genes produce their observed 

 effects: by differential acceleration of 

 various reactions in the organism" or 

 "In such a complex system of successive 

 and 'competing' reactions the differential 

 acceleration of certain ones can produce 

 great, and apparently complete differences 

 in the end results. It is not at all impossi- 

 ble that the metabolic and morphogenetic 

 differences among species, individuals and 

 tissues may be entirely due to differential 

 acceleration, by specific catalysts, of the 

 infinite variety of 'spontaneous' reactions 

 possible to the components of protoplasm. ' ' 

 Readers of our papers (notably '2.0b and 

 'zza) will be familiar with these conclu- 

 sions, even to the expression "competing 

 reactions." One of the writer's papers 

 ('2.3c) is entitled "Contributions to the 

 theory of differentially accelerated reac- 

 tions" (literally "tuned reaction-veloci- 

 ties"). It is further remarkable that 

 proceeding in his analysis Plunkett comes 

 to views regarding the relation of these 

 genie reactions to morphological locali- 

 zations, approaching very closely those 

 which the present author developed in 

 his book, which was through press when 

 Plunkett's paper appeared. This en- 

 courages the present writer to believe 

 that after all his theory of heredity is 

 "sound genetics and sound physiology." 



D. EVIDENCE DERIVED FROM THE STUDY 



OF DEVELOPMENT OF MENDELIAN 



CHARACTERS 



In reviewing the case of multiple allelo- 

 morphs for the pigmentation of Lymantria 

 we have already met with the study of 

 Mendelian characters during development. 

 A number of other facts are known, which 



furnish further insight into the mode of 

 action of the gene. Two students of 

 Haecker (who introduced for this type of 

 study the term phenogenetics) Pernitzsch 

 and Schnakenbek ('13) showed that the 

 difference between normal and albinotic 

 axolotls is mainly a result of different 

 rates of growth and multiplication of the 

 melanophores and xanthophores. The 

 present writer ('2.0, Z3O found that the 

 differently colored parts of the pattern of 

 a butterfly wing are the product of differ- 

 ent rates of differentiation of the scales, 

 with the effect that the scales in different 

 parts of the pattern are ready for the 

 deposition of pigments at different times. 

 This demonstrated the presence of a series 

 of differently timed reactions working 

 together in a definite way (see detailed 

 discussion, 'zya). In a paper on the 

 color-types of the fish Oryzias Goodrich 

 C27) finds that the different Mendelian 

 phenotypes are produced by deposition of 

 different quantities of pigment in given 

 numbers of cells. This might of course 

 be expressed in terms of reaction velocities. 

 In this section such general studies on 

 development might also be mentioned as 

 do not relate to definite genes but rather 

 to the general un analyzed genotype. 

 We think of the work of Stockard, New- 

 man, Harrison, Spemann, Brandt. Here 

 many instances are found demonstrating 

 the importance of timed reaction-veloci- 

 ties in connection with the genotypic 

 constitution. (For particulars and discus- 

 sion see Goldschmidt, '2.7a.) 



E. EVIDENCE DERIVED FROM 

 HETEROZYGOSITY 



There is, I believe, a consensus of 

 opinion that dominance is not a property 

 of an individual gene but one of the results 

 of the interaction of the genes, including 

 the one in question, in producing the 



