HEREDITY 239 



tions of trivial characters. It may happen that the male and 

 female parents that mate display different trivial, or Mendelian 

 characters, but the definition of heredity given here is not thereby 

 invalidated — among the offspring, or the offspring of the offspring 

 of these parents, will be individuals that display not only the 

 specific or racial characters but also the trivial, or Mendelian 

 characters of one or other parent. Therefore the whole develop- 

 mental process by which two ova became two parents are the same 

 processes by which some offspring become individuals of one 

 parental category and other offspring become individuals of the 

 other parental category. 



And the hypothesis by means of which we (provisionally, and 

 for expository reasons) *' explain " the " transmission " of Men- 

 delian characters is that the specific developmental process is the 

 result of operation of an ensemble of causal agencies, E, all these 

 being integrated so as to be one agency, while the developmental 

 process that leads to the appearance of a Mendelian character is 

 due to the result of operation of another agency not integrated 

 into the ensemble but capable of being *' loosely attached " to 

 the latter. That is the reason that, among the progeny, there 

 may be individuals displaying many combinations of the 

 loose, Mendelian characters displayed by the two parents. Of 

 course, this is not a working hypothesis of Mendelian develop- 

 mental processes since it does not attempt to investigate the 

 nature of the ensemble, E, or of the developmental agencies 

 that are responsible for the appearances of the Mendelian 

 characters. 



83^. The " Transmission " of Characters. It is only for 

 convenience that we say that the parent '^ transmits " certain 

 characters to the offspring. Consider the very simplest case of 

 a racial history — that of a protozoan that reproduces by simple 

 fission. That the mode of reproduction is asexual makes con- 

 sideration of what happens simple. Sex only complicates the 

 discussion without changing the essential ideas. 



Here we start with the " mother-cell " (or organism), Fq 

 (Fig. 33). This divides (or reproduces), giving rise to the 

 '' daughter-cells," Fi, F^, Fj again divides, giving rise to the 

 granddaughter cells, Fg F^ and so on. There is, of course, a 

 short phase of development after each division during which 

 the nuclear constituents of the daughter, granddaughter, etc., 



