Transmission of Characters through Heredity. 103 



heredity. Many of these acts, which older naturalists explained 

 1 > Y that evasi ve word " instinctive," may be the mere unconscious 

 outcome of organization, comparable to vegetative growth ; but 

 insects exhibit all degrees of intelligence in their habits and 

 actions, and they perform acts which, however voluntary and, 

 as 1 believe, conscious in many cases, as in that of our Yucca 

 Moth, could not be performed were the tendency not inherited. 

 Every larva which spins or constructs a hibernaculum, or a 

 cocoon in which to undergo its transformations, exemplifies 

 the potent power of heredity in transmitting acquired peculiar- 

 ities. A hundred species of parasitic larva?, e. #., of the family 

 Braconidse, which in themselves are almost or quite indistin- 

 guishable from one another structurally, will nevertheless con- 

 struct a hundred distinctive cocoons differing in form, in text- 

 ure, in color, and in marking each characteristic of its own 

 species and in many instances showing remarkable architectural 

 peculiarities. These are purely mechanical structures, and can 

 have little or nothing to do with the mere organization or form 

 or structure of the larva, but they illustrate in the most convinc- 

 ing manner the fact that the tendency to construct and the power 

 to construct the cocoon after some definite plan must be fixed 

 by heredity, since there is no other way of accounting for it. 

 This fact alone, which no one seems to have thought of in the 

 discussion, should be sufficient to confound the advocates of the 

 non-transmissibility of acquired characteristics. 



Thus to my view modification has gone on in the past, as it 

 is going on at the present time, primarily through heredity in 

 the insect world. I recognize the physical influence of environ- 

 ment; I recognize the effect of the interrelation of organisms; 

 I recognize, even to a degree that few others do, the psychic in- 

 fluence, especially in higher organisms the power of mind, 

 will, effort, or the action of the individual as contradistinguished 

 from the action of the environment ; 1 recognize the influence 

 of natural selection, properly limited ; but above all, as making 

 effective' and as fixing and accumulating the various modifica- 

 tions due to these or whatever other influences, I recognize the 

 power of heredity, without which only the first of the influences 

 mentioned can be permanently operative. 



Let us stop for a moment to ponder what the intricate adjust- 

 ments between plants and animals, and especially between 

 plants and insects, mean, when these have become so profoundly 

 modified by each other that their present existence actual Iv de- 



