200 EVOLUTION AND ANIMAL LIFE 



too much. For example, Professor Cope argues very ably that bones 

 are lengthened by both stretch and impact, and that modifications 

 thus produced are inherited. Even granting that this is true, how 

 would it be possible for this process of lengthening to cease, since in 

 active animals the stretch and impact must be continual? Professor 

 Cope answers that the growth ceases when 'equilibrium' is reached. 

 I confess that I cannot understand this explanation, since the assumed 

 stimulus to growth must be continual. But, granting again that 

 growth may stop when an animal's legs become long enough to 'sat- 

 isfy its needs,' how on this principle are we to account for the shorten- 

 ing of legs, as, for example, in the turnspit dog and the ancon sheep 

 and numberless cases occurring in nature? If any one species was 

 able, by taking thought of mechanical stresses and strains, to add one 

 cubit unto its stature, how could the same stresses and strains be 

 invoked to decrease its stature? 



' These evidences are, I know, not the strongest ones which can be 

 adduced in support of the Lamarckian factors. There are at present 

 a relatively small number of such arguments which seem to be valid 

 and the great force of which I fully admit. But the cases which I have 







cited are, I believe, fair samples of the majority of the evidences so 

 far presented, and in the face of such 'evidence' it is not surprising 

 that one who is himself a profound student of the subject and a con- 

 vinced Lamarckian prays that the Lamarckian theory may be deliv- 

 ered from its friends." * 



As to the inheritance of the effects of extrinsic forces on 

 the individual, we find little in the way of direct evidence. 



In all the members of the large family of flounders and soles, 

 the adult fish rests flat on the bottom and swims on its side, the 

 cranium being twisted so that both eyes appear on the upper 

 side. As a rule color cells are developed on the upper side only, 

 the lower cells remaining largely uncolored or white. In the 

 young of all species the head is symmetrical, both eyes being 

 normally situated, and the fish swims vertically in the water. 

 Little by little, as development goes on, the fish turns over to 

 one side, and the eye of the lower side passes around or through 

 the forehead to join its fellow on the upper side. On the upper 

 side pigment cells develop, while on the lower side they remain 



'H. F. Osborn, "Evolution and Heredity," Wood's Holl Biological 

 Lectures, 1890. 



