THE CHROMOSOMES IN HEREDITY. ' 243 



sufficient in the present state of our knowledge to bring many 

 cases of apparently continuous variation into definite relation with 

 strictly Mendelian cases ; but, on the other hand, it seems prob- 

 able, as already noted (p. 221), that the individual variation in 

 many characters now thought to be strictly Mendelian may prove 

 to be due to the existence in the species of many variations of 

 what may be regarded as the type allelomorphs, accompanying 

 similar variations of the homologous chromatin entities represent- 

 ing those types. 



2. First Crosses that Breed True. - - It is obvious that in the 

 germ-cells of true-breeding hybrids 1 there can be no qualitative 

 reduction. In the normal process synapsis must be accounted 

 for by the assumption of an affinity existing between maternal 

 and paternal homologues, and conversely reduction is the dis- 

 appearance of that affinity or its neutralization by some greater 

 force. Now in Hicmchun the characters of the hybrid are fre- 

 quently intermediate between those of the two parents, showing 

 that both allelomorphs (or chromatin-entities) are at work, but 

 on self fertilization there is no resolution of allelomorphs (reduc- 

 tion division). On the contrary, all the germ-cells are equivalent, 

 as shown by the fact that all combinations produce similar off- 

 spring which in turn are similar to the parent. The suggestion 

 made by Bateson in another connection, that " if one allelomorph 

 were alone produced by the male and the other by the female we 

 should have a species consisting only of heterozygotes," which 

 would come true as long as bred together, at first sight seems 

 logically applicable to these cases. For such an idea, however, 

 we can find no cytological justification, since if any reduction 

 occurs both chromosomes occur in both male and female germ- 

 cells in equal numbers ; and further, the evidence is in favor of a 

 great variety of combinations of maternal and paternal chromo- 

 somes in the germ-cells so that the exact chromosome group of 

 a hybrid parent could hardly be duplicated except by fusion of 

 the very pair of cells separated by the reducing division. A 

 more plausible explanation from the cytological standpoint is that 

 the union of the chromosomes in synapsis is so firm that no 

 reduction can take place, i. c., that in each case, a paternal and 



1 Cf. Mendel's experiments on Hiemciiim. 



