No. 627] 



ADAPTATION 



355 



are dealing with a field in which ever more minute differ- 

 ences are being distinguished— many of them by purely 

 subjective tests— and one in which the ratio of inference 

 to observed fact is ever lengthening. May it not be that 

 we have here hitherto unsuspected possibilities of self- 

 deception on the part of even our most competent inves- 

 tigators? The subject is one which seems to me to de- 

 serve more attention than it has received. 



On the w^liole, we are not compelled to assume the 

 existence of any more preformation than can be experi- 

 mentally demonstrated. And it may be regarded as 

 settled that we have no parcelling out of "deter- 

 minants" to appropriate cells during ontogeny, such as 

 Weismann imagined. The "sex chromosomes," which 

 seem to be the best authenticated instances of material 

 bearers of hereditary traits, do not x><iss into definite 

 body cells in the course of development and thus give 

 rise to the primary and secondary organs of sex. Kather 

 are they to be found distributed in every cell of the body. 

 The assumption that they set free their characteristic 

 determinants only in particular cells has no experimental 

 or observational foundation. 



Now, I am quite aware that any such " ' iiii r.i-sclcctiou " 

 hj-pothesis of organic regulation as lias her.' h.M'ii advo- 

 cated will be rejected l)y a large proportion of l)i()l()gists 

 on the ground that it is entirely sui)erHuons. N^arious 

 types of self-regulatinu- niec-lianisnis have been found in 

 the non-living world, and the phenomena of growth and 

 regeneration have long l)een known to he duijlicated in 

 crystals. Przibram has gone to eonsiderahle lenuths in 

 pointing out analogies between the hehaxior ot the so- 

 called "fluid crystals" and that ot a n-vneratinu- oi-an- 



