626 TRANSACTIONS OF SECTION D. 



lay too much stress upon them if it were not tor the fact that they are so com- 

 pletely confirmatory of the results obtained by similar methods in the animal 

 kingdom. 



i submit to you that evidence is forthcoming that external conditions 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 conditions 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 connect 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 tttockard; 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 conditions 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 important of the two. More im- 

 portant 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 resulted 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 hi 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 zoolo- 

 gist. 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 

 perhaps I may be allowed to allude to one or two generalisations which appear to 

 me to be most suggestive. 



We shall all agree that, at the bottom, production and change of form is due 

 to increase or diminution of the activities of groups of cells, and we are awaro 

 that in the higher animals change of structure is not altogether a local affair, but 

 carries with it certain consequences in the nature of correlated changes in other 

 parts of the body. If we are to make any progress in the study of morphogeny, 

 we ought to have as exact ideas as possible as to what we mean when we ^peak of 

 the activities of cells and of correlation. On these subjects physiology supplies 

 us with ideas much more exact than those derived from morphology. 



It is, perhaps, too sweeping a generalisation to assert that the life of any 

 given animal is the expression of the sum of the activities of the enzymes con- 

 tained in it, but it seems well established that the activities of cells are, if not 

 wholly, at all events largely, the result of the actions of the various kinds of 

 enzymes held in combination by their living protoplasm. These enzymes are 

 highly susceptible to the influence of physical and chemical media, and it is 

 because of this susceptibility that the organism responds to changes in the en- 

 vironment, as is clearly illustrated in a. particular case by Tower's experiments 

 on the production of colour changes in potato-beetles. Bayliss and Starling have 

 shown that in lower animals, protozoa and sponges, in which no nervous system 

 has been developed, the response of the organism to the environment is effected by 



