360 THE ZOOLOGIST. 



enzymes sufficient to insure the due succession of all its develop- 

 mental stages as well as of its adult structure and functions. And 

 as the number of blastomeres increases, and the need for co-ordination 

 of form and function arises, before ever the rudiments of a nervous 

 system are differentiated, it is necessary to assume that there is also 

 a stock of appropriate hormones to supply the chemical nexus 

 between the different parts of the embryo. The only alternative is 

 to suppose that they are synthesised as required in the course of 

 development. There are grave objections to this supposition. All 

 the evidence at our disposal goes to show that the potentialities of 

 germ-cells are determined at the close of the maturation divisions. 

 Following the physiological line of argument, it must be allowed that 

 in this connection "potentiality" can mean nothing else than chemi- 

 cal constitution. If we admit this, we admit the validity of the 

 theory advanced by more than one physiologist, that heritable 

 " characters " or " tendencies " must be identified with the enzymes 

 carried in the germ-cells. If this be a true representation of the 

 facts, and if the most fundamental and primitive bond between one 

 part of an organism and another is a chemical bond, it can hardly be 

 the case that germ-cells — which, inter alia, are the most primitive, 

 in the sense of being the least differentiated, cells in the body — 

 should be the only cells which are exempt from the chemical 

 influences which go to make up the co-ordinate life of the organism. 

 It would seem, therefore, that there is some theoretical justification 

 for the inheritance of induced modifications, provided that these are 

 of such a kind as to react chemically on the enzymes contained in 

 the germ -cells. 



One further idea that suggests itself to me and I have done. Is 

 it possible that different kinds of enzymes exercise an inhibiting 

 influence on one another; that germ-cells are "undifferentiated" 

 because they contain a large number of enzymes, none of which can 

 show their activities in the presence of others, and that what we call 

 " differentiation " consists in the segregation of the different kinds 

 into separate cells, or perhaps, prior to cell-formation, into different 

 parts of the fertilised ovum, giving rise to the phenomenon known to 

 us as prelocalisation ? The idea is purely speculative ; but, if it 

 could be shown to have any warrant, it would go far to assist us in 

 getting an understanding of the laws of the production of form. 



I have been wandering in territories outside my own province, 

 and I shall certainly be told that I have lost my way. But my 

 thesis has been that morphology, if it is to make useful progress, 

 must come out of its reserves and explore new ground. To explore 

 is to tread unknown paths, and one is likely to lose one's way in the 

 unknown. To stay at home in the environment of familiar ideas is 

 no doubt a safe course, but it does not make for advancement. 

 Morphology, I believe, has as great a future before it as it has a past 

 behind it, but it can only realise that future by leaving its old home, 

 with all its comfortable furniture of well-worn rules and methods, 

 and embarking on a journey, the first stages of which will certainly 

 be uncomfortable and the end is far to seek. 



