770 EEPORT — 1889. 



mediation of any external force or influence acting directly upon the soma. 

 Further, this must have endured throughout a succession of countless individual 

 forms and species, extending over we knovv not hov? many thousands of years, 

 and through the various geological and climatic changes which have affected the 

 glote. 



The power of producing these variations would therefore, on this theory, have 

 Ijeen from the heginning- innate to the germ-plasm, and uninfluenced in any way 

 by its surroundings. Variations would have arisen spontaneously in it, and, for 

 anything that we know, as it were by accident, and without a definite purport or 

 object. But whether such variations would be of service or dis-service could not 

 be ascertained until after their appearance in the soma had subjected them to the 

 test of the conditions of life and the environment. 



Let us now glance at the other side of the question. All biologists will, I 

 suppose, accept the proposition that the individual soma is influenced or modified 

 by its environment or surroundings. Now, if on the basis of this proposition the 

 theory be grafted that modifications or variations thus produced are capable of so 

 affecting the germ-plasm of the individual in whom the variation arises as to be 

 transmitted to its ott'spring — and I have already given cases in point — then such 

 variations might be perpetuated. If the modification is of service, then presumably 

 it will add to the vitability of the individual, and through the interaction between 

 the soma and the germ-plasm, in connection with their respective nutritive changes, 

 will so affect the latter as to lead to its being transmitted to the oflspring. From 

 this point of view the environment would, as it were, determine and regulate the 

 nature of those variations which are to become hereditary, and the possibility of 

 ■variations arising which are likely to prove useful becomes greater than on the 

 theory that the soma exercises no influence on the germ-plasm. Hence I am unable 

 to accept the proposition that somatogenic characters are not transmitted, and I 

 cannot but think that they form an important factor in the production of here- 

 ditary characters. 



To reject the influence which the use and disuse of parts may exercise both on 

 the individual and on his off'spring is like looking at an object with only a single 

 eye. The morphological aspect of organic structure is undoubtedly of fundamental 

 importance. But it should not be forgotten that tissues and organs, in addition to 

 their subjection to the principles of development and descent, have to discliarge 

 certain specific purposes and functions, and that structural modifications arise in 

 them in correlation with the uses to which they are put, so as to adapt them to 

 perform modified duties. It may be difficult to assign the exact value which phy- 

 siological adaptation can exercise in the perpetuation of variations. If the habit or 

 external condition which has produced a variation continues to be practised, then, 

 in all probability, the variation would be intensified in successive generations. But 

 should the habit cease or the external condition be changed, then, although the 

 variation might continue to be for a time perpetuated by descent, it would probably 

 become less strongly marked and perhaps ultimately disappear. One could also con- 

 ceive that the introduction of a new habit or external condition the effect of which 

 would be to produce a variation in a direction different from that which had origin- 

 ally been acquired, would tend to neutralise the influence of descent in the trans- 

 mission of the older character. 



By accepting the theory that somatogenic characters are transmitted we obtain 

 a more ready explanation, how men belonging to a race living in one climate or 

 part of the globe can adapt themselves to a climate of a different kind. On the 

 theory of the non-transmissibility of these acquired characters, long periods of 

 years would have to elapse before the process of adaptation could be effected. The 

 weaker examples, on this theory, would have liad to have died out, and the racial 

 variety would require to have been produced by the selection of variations arising" 

 slowly, and requiring one knows not how many hundreds or thousands of years to 

 produce a race which could adapt itself to its new environment. We know, 

 however, that this process of the dying out of the weakest and the selection of the 

 strongest is not necessary to produce a race which possesses well-recognisable 

 physical characters. For most of lis can, I think, distinguish the nationality of a 



