Influence of Environment 2ipon the Organism. 4GP> 



This general action, followed, of course, by others, must also 

 be allowed. 



(7.) While anything of the nature of cataclysmic action is 

 regarded with just suspicion, there can be no doubt that 

 unusual environmental conditions may affect crowds of 

 organisms in a somewhat wholesale way. Thus Eupert 

 Jones (212) gives a list of the various conditions which may 

 affect a whole series of organisms, or even a fauna. 



(8.) Lastly, it is enough to notice, that if we regard the 

 environment as comprising animate, as well as inanimate, 

 external influences, the effect of multiplication of rival com- 

 petitors within a species, and of inimical members of other 

 genera, may affect the organism not only directly, but also 

 indirectly, through the inanimate environment. This category 

 of influence is familiarly included in the conception of the 

 struggle for existence, or of natural selection. 



10. Periods of Environmental Influence. — It is also in- 

 structive to classify the influences in order of time. (1.) 

 Influences begin to operate upon the germ-cells in situ. 

 According to its position, the ovum will be subject to varying 

 nutritive conditions. In some cases the ultimate ova are the 

 most successively nourished individuals among a crowd of 

 unsuccessful competitors. In the primitive hermaphroditism, 

 said to occur in the history of many unisexual forms, the 

 predominant nutrition of certain areas is doubtless of im- 

 portance. Sutton (pp. cit.) maintains the general proposition 

 that hermaphroditism is primitive; that hypertrophy is at 

 least one of the processes in the differentiation of the separate 

 sexes ; and that " reproduction in Vertebrata, so far as is 

 known, is impossible, unless hypertrophy of one set of organs 

 occurs." Eoux {op. cit., 222) has shown that definite injuries 

 to the ovum produce definite defects in the embryo. 



(2.) The stimulus of the male element is another influence 

 ah extra on which various naturalists {e.g., Treviranus, 259 ; 

 but especially Weismann, 244) have laid emphasis. The case 

 of bees, as usually interpreted, is a familiar illustration of 

 importance in this connection. The difference in the 

 maturation of parthenogenetic and normal ova (established 

 by Weismann and others) ought also to be noted. It is again 



