1064 The American Naturalist. [December. 
es when he is more active than the female ; and 
hence more under the stimulus of use. 
The manner in which influences which have aflfected the general 
structure are introduced into the germ cells remains the most 
difficult problem of biology. For its explanation we have nothing 
as yet but hypotheses. The one which has seemed to me to be the 
most reasonable belongs to the field of molecular physics, and it 
must be long before it is either proved or disproved. I have 
termed it a " dynamic theory," and it is in some respects similar 
to that subsequently proposed by Hacckel under the name of the 
" perigenesis of the plastidulc." I have already referred to the 
phenomena of the building or growth of the added characters 
which constitute progressive evolution as evidence of the exist- 
ence of a peculiar species of energy which I termed bathmism. 
This is to be explained as a mode of motion of the molecules of 
living protoplasm, by which the latter build tissue at particular 
points, and do not do so at other points. This action is most 
easily observed in the beginnings of growth, as in the segmenta- 
tion of the oosperm, the formation of the blastodermic layers, of 
the gastrula, of the primitive groove, etc. In the meroblastic 
embryo the energy is evidently in excess at one part of the 
o6sperm, and in defect at another. This is a simple example of 
the " location of growth force or bathmism." In all folding or in- 
vagination, there is excess of growth at the region which becomes 
the convex face of the fold ; or a location or especial activity of 
bathmism at that point. All modifications of form can be thus 
traced to activity of this energy at particular points. A basis is 
thus laid for a more or less complex organism, and the channels 
of nutritive pabulum being once established, the location or dis- 
tribution of the energy is assured in the directions in wliich they 
lead. Thus with the establishment of circulating channels nutri- 
tion is definitely guided to particular points. It is evident that 
on this hypothesis the bases of evolutionary change are laid in 
the embryonic tissues, where indeed bathmism displays its activity 
in producing the base forms on which all subsequent structure is 
moulded. 
