638 Vehicles of the Hereditary Characters. 
support the main thesis, and attach little importance to 
the transportation hypothesis. 
GALTON supposes that the various cells of the body 
are originally represented by special material vehicles. 
These vehicles combine to constitute the stirp which is 
practically the same as the idioplasma. 1 Many more ve- 
hicles must, however, be present in the germ than there 
are actual types of cells. The remaining latent particles 
play a still more important part in GALTON 's theory than 
they do in DARWIN'S, both in the explanation of onto- 
genetic development and of atavism. The germ sub- 
stance is handed down unchanged in the cell divisions 
as well as in the multiplication of the individuals. It 
is only under certain circumstances that changes appear 
in it ; an assumption, which is obviously necessary for 
the explanation of the transformation of species. 
In an extraordinarily clearly written book on hered- 
ity W. K. BROOKS has also suggested a modification of 
the theory of pangenesis. 2 He does not reject the whole 
transportation hypothesis, but confines it to the trans- 
portation of a few particles in special cases, especially 
when the organism undergoes any change, whether from 
external or internal causes. A change in the environment 
of a cell induces it to throw off particles, and therefore 
to transmit to the offspring of the plant a tendency to 
deviate in the corresponding parts of the body in the 
same way (p. 83). The male germ cells are particularly 
adapted to the purpose of collecting these particles and 
transmitting them to the female germ cells. If a change 
has once become heritable through the medium of trans- 
1 FRANCIS GALTON, 'A Theory of Heredity, 1875. 
~\\ T . K. BROOKS. The Law of Heredity, a Study of the Cause of 
Variation and the Origin of Lh'ing Organisms, i<S83. See especially 
pp. 80- TOO, 319, 327, etc. 
