450 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



is similar to that which produces reflexes may be also 

 reasonably supposed. How the record of these move- 

 ments become reflexes, Us concentrated in a reproduc- 

 tive cell, is a question to be solved only in a more ad- 

 vanced stage of knowledge of organic physics than we 

 now possess. 



Speculation in this direction takes the following 

 forms. According to one view the energy or molecu- 

 lar movement must be transmitted to the germ-plasma 

 through a material or molecular basis. This basis, it 

 may be supposed, must be that which receives the 

 mechanical impression which is to produce a corre- 

 sponding modification of growth-energy in the ovum 

 or spermatozooid ; that is, in the case of a modified 

 bone-articulation, particles of matter must pass from 

 the latter through the medium of the circulation to 

 the reproductive cells. The alternative hypothesis is, 

 that the energy which causes the active region to make 

 or omit to make a given movement, the result of which 

 is to be structural modification in the young, is im- 

 pressed through protoplasmic channels on the germ- 

 cells of either sex. In this case the transmission of 

 particles of matter is not necessary, as material connec- 

 tion through the cells, nervous or other, already exists. 



To the first of these points of view belong the pan- 

 genesis theory of Darwin, and the modified pangenesis 

 of Weismann. These hypotheses present the difficulty 

 that we must conceive of each particle or "gemmule" 

 derived from a given part of the organism finding its 

 way through the circulation to its exact place in the 

 growing embryo ; or otherwise, of transmitting its pe- 

 culiar mode of motion to the correct molecules of the 

 embryo, without error as to locality. The difficulties 

 to be encountered in accomplishing such a feat seem 



