PRESIDENTIAL ADDRESS. 415 



such e,^planation will fit the case we are considering. For the additional 

 hydroccele shows all degrees of development, and according to the degree of its 

 development is the amount of influence which it exercises on the tissues of the 

 right side. When it is comparatively small it may cause the formation of an 

 amniotic invagination but may not be able to inhibit the formation of pedicel- 

 larise, so that the characteristics of both sides of the larva are present together 

 on the same side, and I have obser\'ed cases where it is still smaller and then it 

 is unable to produce even an amniotic invagination, although it shows by its 

 lobes, &c., that it is an unmistakable hydroccele. 



These observations show that we must accept the view that this marvellous 

 structure, when once established, really does effect these wonderful transforma- 

 tions in what are relatively indifferent tissues by the materials which it exudes, 

 and it seems impossible to suggest any modification of the theory of the 

 entelechy which will fit this case. We can gather a suggestion of the possible 

 answer to an objection raised by Driesch to the theory of organ-forming sub- 

 stances. Driesch says in effect this : If, considering the case of the regenera- 

 tion of the legs of the tadpole when they have been cut off, we assume the 

 existence of a material with the capacity of developing into a leg, how are we 

 to explain the circumstance that when the leg is cut off at the knee the stump 

 containing this supposititious substance regenerates not a whole leg but only 

 the missing part ? Now we find that the formation of a second hydroccele can 

 not only effect great changes in the adjacent tissues; it can also inhibit the 

 formation of pedicellarise. So we may well believe that when regeneration of an 

 organ takes place, the presence of a portion of the organ to be regenerated may 

 inhibit the organ-forming substance from producing a second edition of the same. 



We cannot close this survey without allowing ourselves to reflect on the light 

 which the fact we have related may throw on the cause of variation, which is 

 one of the root problems of biology. We have been gradually led to view the 

 nucleus as a storehouse of all the characters of the species, and to look for the 

 cause of the first differentiations seen in development in the modification of the 

 cytoplasm through the emission of substances from the nucleus ; but to attribute 

 much of the later development to the modification of one organ through the 

 influence of materials emitted into the body-fluids by another organ, so that we 

 may compare the organs of the growing body to an assemblage of semi- 

 independent organisms which constitute an environment for one another. We 

 all know from medical evidence that there exist certain organs of the body — ■ 

 the so-called ductless glands or endoceine organs — whose secretions have 

 enormous influence both on the growth and the function of all the other organs 

 of the body. The question then inevitably occurs to our minds whether all the 

 organs of the body may not exercise the same kind of influence on each other to 

 a lesser degree. As St. Paul puts it : 'If one member suffers, all the rest of 

 the body suffers with it.' Now, Dr. Cunningham put forward the idea that 

 when an organ becomes modified in response to new conditions — as we know 

 that organs can become modified — its chemical influence on other organs 

 changes, and amongst others its influence on the genital cells. The substances 

 which it emits are, we may suppose, taken up by these cells, and perhaps stored 

 up by them in the genital nuclei. When these substances have been changed 

 by reaction with a changed environment, these changed substances will be 

 absorbed by the genital cells, and when these cells develop into new organisms 

 the altered materials which they emit into the cytoplasm will tend to produce 

 in it the same alterations as were produced by the changed environment even 

 before the latter can act. In this way characters originally acquired in 

 response to a changed environment may be conceived to become ingrained, as it 

 were, in the organism. It has always been one of the great difliculties of the 

 theory of the inheritance of acquired characters to conceive how a change in an 

 external organ could, so to speak, cause a corresponding change in a genital cell; 

 and if the change in the external organ be a mere mutilation, such as is produced 

 by cutting off the tail of a mouse, for example, this difficulty is insurmount- 

 able, and there is no evidence whatever that such mutilations are ever inlierited. 

 And yet the negative evidence derived from such experiments has been adduced 

 to prove the impossibility of the inheritance of acquired qualities ! But when 



