REVIEW. Se 
little truth.” This is the key note of the book before us, which 
is therefore worthy of very careful consideration, however unsatis- 
factory it may prove to be as an explanation of the great prob- 
lem of heredity. 
The theory proposed in this book is a modification of Dar- 
win’s hypothesis of pangenesis, reconstructed with a view of 
avoiding the many difficulties in the way of that hypothesis. 
Brooks’s theory, very briefly stated, is as follows :—1. The union 
of two sexual elements gives variability ; 2. In all multicellular 
organisms the ovum and the male cell have gradually become 
specialised in different directions ; 3. The ovum has acquired a 
very complex organisation, and contains material particles of 
some kind corresponding to each of the hereditary species 
characteristics; 4. The ovarian ova of the offspring are the 
direct and unmodified descendants of the parent ovum; 5. Each 
cell in the body has the power of throwing off minute germs. 
During the evolution of the species, these cells have acquired 
distinctive functions adapted to the conditions under which they 
are placed. When the function of a cell is disturbed through a 
change in its environment, it throws off small particles, which 
Seeremerserins or‘ semmules” of this. particular cell. 6. These 
germs may be carried to all parts of the body, and penetrate to 
an ovum or to a bud; but the male cell has acquired a peculiar 
power to gather and store upgerms. 7. When the impregnation 
occurs, each gemmule impregnates that particle of the ovum 
which will give rise in the offspring to the cell corresponding 
to the one which produced the gemmule, or else it unites with a 
closely related particle, destined to produce a closely related cell. 
8. In the body of the offspring this cell will be a hybrid, and 
tend to vary. 9. The ovarian ova of the offspring inherit the 
properties of the fertilised ovum directly, and the organisms 
to which they give rise will tend to vary in the same manner. 
10. A cell which has varied will continue to throw off gemmules, 
and so cause variations in the corresponding parts of the bodies 
of descendants, until a favourable variation is seized upon by 
natural selection. 11. The ovarian ova will directly inherit the 
selected variation, and will transmit it as an hereditary race 
characteristic without the agency of gemmules. 12. The occur- 
ence of a variation, but not its precise character, is due to the 
direct action of external conditions. 
These positions Professor Brooks endeavours to establish by a 
great number of facts, taken almost exclusively from Darwin. 
He first combats the view that sexual elements play similar 
parts in reproduction, and the objection seems to be well taken ; 
though, when he says that it cannot be shown that either sex 
may transmit azy characteristic whatever, he pushes his objection 
too far, as is demonstrated by a multitude of facts in the breed- 
ing of domestic animals. 
Having stated the theory, the author devotes a large part of 
his book to the evidence in its favour. From the study of hybrids 
he concludes that hybrids and mongrels are highly variable; that 
