96 Proceedings of Royal Society of Edinburgh. [sess. 
attached sufficient importance. The very important part of Galton’s 
theory will be discussed in its proper place ; it is not included in the 
series of pangenetic hypotheses. Galton is, in fact, one of the 
numerous biologists who have suggested the continuity of the ger- 
minal protoplasm. He is included at this stage, however, because 
he admitted as a subsidiary hypothesis a limited amount of pan- 
genesis. To account for those cases which suggest that characters 
acquired by the individual parent are “faintly heritable,” Galton 
supposed that “ each cell may throw off a few germs that find their 
way into the circulation, and have thereby a chance of occasionally 
finding their way to the sexual elements, and of becoming naturalised 
among them.” This part of his theory is obviously a cautious admis- 
sion of limited pangenesis to account for a limited number of doubtful 
cases. 
Brooks' Theory . — In 1883, in his valuable work entitled The Law 
of Hei'edity, Professor W. K. Brooks gave full expression to a modi- 
fication of Darwin’s view of pangenesis. The main positions, which 
are here relevant, may be summarised as follows, almost in the 
author’s words : — 
(1) The male and female cells are specialised in different directions; 
their union gives variability. 
(2) The ovum is a cell which has gradually acquired a compli- 
cated organisation, and which contains material particles of 
some kind to correspond to each of the hereditary charac- 
teristics of the species. 
(3) The ovum reproducing its like, as other cells, gives rise not 
only to the divergent cells of the organism, but also to cells 
like itself. 
(4) Each cell of the body has the power to throw off minute 
germs. When, through a change in its environment, its 
functions are disturbed, and its conditions of life become 
unfavourable, it throws off small particles which are the 
germs or gemmules of this particular cell. 
(5) These germs may be carried to all parts of the body. They 
may penetrate to an ovarian ovum or to a bud, but the male 
cell has gradually .acquired, as its especial and distinctive 
function, a peculiar power to gather and store up germs. 
(6) In fertilisation each gemmule unites with that particle of the 
