The President's Address. By H. C. Sorhij, F.RS., ttu 119 



Gemmnles are supposed to be thrown off by every cell or unit, not 

 only during the adult state, but during all the stages of develop- 

 ment. He assumes that the gemmules in their dormant state have 

 a mutual affinity for each other, leading to their aggregation into 

 buds or into the sexual elements. These assumptions constitute 

 the provisional hypothesis which he calls Pangenesis." 



In order to form some opinion as to whether the ultimate 

 molecules of organic matter are of such a size as to make this 

 theory possible or probable, it is necessary to form some idea as 

 to the number of such molecules that may be united to make 

 one gemmule. It must be very considerable, or else it seems 

 difficult to understand how they could vary enough to explain the 

 inheritance of many characters. Perhaps, for the sake of argument, 

 we may assume that on an average each contains something like 

 a million. Varying numbers, chemical constitution, and arrange- 

 ment, would in such a case allow of an almost infinite variety ; but 

 of course we are so profoundly ignorant of many necessary details 

 that this number can be looked upon only as a rough illustration of 

 the application of a general method of study. On this supposition 

 one thousand such gemmules massed together would form a sphere 

 just distinctly visible with our highest and best magnifying powers. 

 If the gemmules were of much greater or of much less magnitude, 

 it appears to me very probable that Darwin's theory would break 

 down from two opposite causes, or would need very considerable 

 modification, because, if much greater, their number would be too 

 few to transmit sufficiently varied characters, and, if much less, 

 they could scarcely contain enough of the ultimate atoms of matter 

 to have a sufficiently varied individual character to transmit, since 

 of the assumed million ultimate molecules only eighteen thousand 

 would be of a true protoplasmic nature, the rest being of water in 

 molecular combination. 



Adopting, then, this size as a basis for calculation, it is easy to 

 form some opinion as to the number of gemmules that might be 

 present in spermatozoa or in ova, assuming them to be their sole 

 or chief constituent. Thus, for example, if we take ooVo of an inch 

 as the mean diameter of a single mammalian spermatozoon, it 

 might contain two and a half millions of such gemmules. If these 

 were lost, destroyed, or fully developed at the rate of one in each 

 second, this number would be exhausted in about one month ; 

 but, since a number of spermatozoa appears to be necessary to 

 produce perfect fertilization, it is quite easy to understand that the 

 number of gemmules introduced into the ovum may be so great 

 that the influence of the male parent may be very marked, even 

 after having been, as regards particular characters, apparently 

 dormant for many years. 



Then, again, adopting ^-J-^-q of an inch as the mean diameter of 



VOL. XV, K 



