No. 567] 



NOTES AND LITERATURE 



191 



assumes that those chromosomes lying nearest the nuclear wall 

 (peripheral) are better nourished than those centrally located, 

 and hence they exert more influence in character formation, and 

 dominating synapsis, produce gametes similar in their hereditary 

 character to the cells of the first generation hybrids, whose char- 

 acter in turn was determined at fertilization by the configuration 

 the chromosomes took in the fusion nucleus. On this theory, 

 reversions, sports, etc., may result from sudden changes in the 

 nuclear configuration. 



Three types of nuclear configuration are assumed to occur in 

 higher organisms, the character and effects of which are synop- 

 tically outlined below. 



1. Interspecific Hybrids. — Usually sterile and intermediate. 

 Chromosomes repel each other and occupy opposite sides of the 

 F i zygote nuclei, exerting equal influence in the ontogeny of F, 

 organisms, explaining why first generation hybrids of this char- 

 acter are always intermediate, little variable and usually sterile. 

 Synapsis often impossible. 



2. Mendelian Crosses. — Abnormally inbred races of domesti- 

 cated animals and plants. F x generation usually intermediate, 

 fertile, dialytic at synapsis. Dominance of certain characters in 

 these hybrids is due to the inherited potentialities of the chromo- 

 somes rather than to their nuclear positions. 



3. Normal Cross-bred Species. — Probably normal in wild 

 species. Hybrids usually vigorous, fertile, and variable. Free 

 intermingling of chromosomes in the fusion nucleus at fertiliza- 

 tion. Nuclear configuration permanent for each individual. 

 Synapsis normal. 



This elaborate and attractive theory, based admittedly to a 

 great degree on assumptions, is advanced by Swingle in the belief 

 that it will help to clarify the problems of heredity, even though 

 he acknowledges it does not help one to arrive at satisfactory 

 explanations. In the reviewer's opinion, however, the field of 

 genetics is already burdened with enough theories of this par- 

 ticular type and the somewhat unnecessary but ever-increasing 

 new additions serve to confuse rather than clarify the ideas of 

 the average student of genetics. Besides, Swingle's assumption 

 that maternal and paternal chromosomes in the cells of F, hybrids 

 repel each other and do not mingle in the F 1 zygote cells is not 

 borne out by the few cytological facts at our command. Kosen- 



