BRITISH ASSOCIATION: ZOOLOGICAL ADDRESS. 357 



especially the transformation of stamens into petals. These experi- 

 ments are still in progress, and it would perhaps be premature to lay 

 too much stress upon them if it were not for the fact that they are so 

 completely confirmatory of the results obtained by similar methods in 

 the animal kingdom. 



I submit to you that evidence is forthcoming that external con- 

 ditions may give rise to inheritable alterations of structure. Not, 

 however, as was once supposed, by producing specific changes in the 

 parental soma, which changes were reflected, so to speak, upon the 

 germ-cells. The new evidence confirms the distinctions drawn by 

 Weismann between somatic and germinal variations. It shows that 

 the former are not inherited, while the latter are ; but it indicates 

 that the germ may be caused to vary by the action of external con- 

 ditions in such a manner as to produce specific changes in the progeny 

 resulting from it. It is no more possible at the present time to con- 

 nect rationally the action of external conditions on the germ- cells 

 with the specific results produced in the progeny than it is possible 

 to connect cause with effect in the experiments of Herbst and 

 Stockard ; but, when we compare these two kinds of experiments, 

 we are no longer able to argue that it is inconceivable that such and 

 such conditions acting on the germ-plasm can produce such and such 

 effects in the next generation of adults. We must accept the 

 evidence that things which appeared inconceivable do in fact happen, 

 and in accepting this we remove a great obstacle from the path of 

 our inquiries, and gain a distinct step in our attempts to discover the 

 laws which determine the production of organic form and structure. 



But such experiments as those which I have mentioned only deal 

 with one aspect of the problem. They tell us about external con- 

 ditions and the effects that they are observed to produce upon the 

 organism. They give us no definite information about the internal 

 changes which, taken together, constitute the response of the 

 organism to external stimuli. As Darwin wrote, there are two 

 factors to be taken into account — the nature of the conditions and 

 the nature of the organism— and the latter is much the more im- 

 portant of the two. More important because the reactions of 

 animals and plants are manifold ; but, on the whole, the changes in 

 the conditions are few and small in amount. Morphology has not 

 succeeded in giving us any positive knowledge of the nature of the 

 organism, and in this matter we must turn for guidance to the 

 physiologists, and ask of them how far recent researches have re- 

 sulted in the discovery of factors competent to account for change of 

 structure. Perhaps the first step in this inquiry is to ask whether 

 there is any evidence of internal chemical changes analogous in their 

 operation to the external physical and chemical changes which we 

 have been dealing with. 



There is a great deal of evidence, but it is extremely difficult to 

 bring it to a focus and to show its relevancy to the particular 

 problems that perplex the zoologist. Moreover, the evidence is of 

 so many different kinds, and each kind is so technical and complex, 

 that it would be absurd to attempt to deal with it at the end of an 

 address that has already been drawn out to sufficient length. But 



