'PHYSIOLOGICAL UNITS' 95 



and in the form which they tend to build themselves into, but 

 having minor differences, work in unison to produce an organism of 

 the species from which they are derived, but work in antagonism to 

 produce copies of their respective pareilt organisms ; and hence 

 ultimately results an organism in which traits of the one are mixed 

 with the traits of the other." ' 



Professor Weldon, in his recently-delivered lectures on "Current 

 Theories of the Hereditary Process," also comes to the conclusion 

 that Weismann's theories concerning the ' sorting of determinants ' 

 are " quite irreconcilable with the facts of the equipotential nature 

 of the blastomeres in the early stages of cell-division [of the ovum] 

 and with the facts of regeneration of lost parts." He adds :— 

 " The changes which subsequently occur in the different cell 

 lineages derived from the fertilised germ-cells are largely due to 

 other factors — viz., the relative positions assumed with regard to 

 each other and to the cell mass by individual cells, and the differ- 

 ences of the incidental stimuli of the environment on differently 

 placed cells (gravity, light and shade, pressure, relative food supply) 

 . . . Hence for normal development and perfect embyrogenesis a 

 very constant and ' correct' environment is necessary." 



Weismann indeed admits that if the power of repair and regene- 

 ration is dependent upon a primary property rather than upon 

 one that has been acquired through ' natural selection ' he would 

 have to give up his position, since he says (Vol. II, p. 19), " in truth 

 if the body were really able to replace, after artificial injury, parts 

 which are never liable to injury in natural conditions, and to do so 

 in a most beautiful and appropriate manner, then there would be 

 nothing for it but at least to regard the faculty of regeneration as a 

 primary power of living creatures, and to think of the organism as 

 like a crystal, which invariably completes itself if it be damaged in 

 any part," 



' The degrees and modes in which the several ancestral traits are mixed, are 

 now being keenly investigated and discussed by two rival schools — one of which 

 favours the views of Francis Galton, and the other the newly-discovered 

 Mendelian hypothesis, which is advocated by Hugo de Vries and Bateson. The 

 views of Galton are favoured by Weldon and Karl Pearson. He believes that 

 the two parents contribute between them J of the total heritage ; the four grand- 

 parents I ; and the eight great grand-parents J of the total heritage, and so on. 

 The differences between the two views seem to depend greatly upon whether 

 the chromosomes always divide " transversely " or " horizontally " (See Weldon 

 "Lancet," Mar. 25, p. 8lo). 



