INSTINCT AS INHERITED HABIT 73 



possibility of " habit " is excluded. Weismann has adduced a 

 number of cases of wonderfully complicated and useful instincts 

 manifested by numerous insects — for instance, those which 

 manifest themselves during the chrysalis stage, and which 

 secure the better protection and preservation of the insect — 

 which express themselves (yrdy once during the life of the insect.^ 

 Here all possibihty of " habit " is excluded ; the inheritance of 

 a modification brought about by use or disuse is impossible in 

 the case of an instinct which manifests itself but once in the 

 course of the hfe-history. Such instincts can only be interpreted 

 in terms of natural selection. Those insects which lacked the 

 instinct to adopt those protective measures during the chrysalis 

 stage would necessarily, through the mechanism of natiiral 

 selection, be more easily destroyed than those which were better 

 protected ; and hence there would eventually survive only those 

 which instinctively adapted themselves to the environing con- 

 ditions. We must remember, also, that the theory of germinal 

 selection fills a gap in the Darwinian theory of natural selection ; 

 for whereas, according to the Darwinian theory, the advanta- 

 geous variations to be selected depend for their production upon 

 chance; according to the theory of germinal selection such 

 variations are induced by intragerminal perturbations, and 

 remain to be selected or not according as they are, or are not, 

 of biological value to the individual or to the species. 



Those instincts, which manifest themselves but once during 

 the course of the individual life, cannot, therefore, be explained 

 as the result of " habit " during that individual life, or as the 

 result of the transmission of habit. There can be no question 

 of this instinct being " strengthened by use." But it may be 

 urged that there are instincts which are strengthened and de- 

 veloped by use in the course of the individual life, and which, 

 handed down from generation to generation, become finally 

 characteristic of the species. Such, it is said, is the instinct of 

 1 Weismann, Vortrage iiber Deszendenztheorie, i. 129 ff. 



