2 
TRANSACTIONS OP THE TEXAS ACADEMY OP SCIENCE. 
presents itself in the form of the following riddles: First, how do the 
vast number of differentiated cell-beings that enter into the formation of 
a complex organism manage to become potentially represented in the ini¬ 
tial germ-cell from which they emanate ? Second, how do the potential 
differentiations inclosed in the germ-cell manage to evolve the adult 
organism ? 
If, in agreement with the cell-theory, the germ-cell is itself looked 
upon as an elementary unicellular being, it would, as such, originally, 
be able to reproduce by means of fissiparous division only its own exact 
kind. How then has it happened that in the course of phylogenetic 
evolution it has been rendered capable of evolving a series of cell-gen¬ 
erations becoming, as organic development in the animal scale proceeds, 
more and more unlike itself, leading ultimately to the formation of such 
incommensurably higher tissues as muscle and brain ? 
These fundamental biological questions are no doubt extremely per¬ 
plexing. But it is clear that organic evolution, as we trace it in its 
manifest morphological outcomes, reveals to us only the gross results of 
a developmental process that is taking place in the hidden sphere of 
molecular activities. Adequately to explain organic evolution, produc¬ 
tive and reproductive; and, indeed, fully to explain any kind of organic 
process, necessitates, therefore, a correct insight into the secret ways by 
means of which molecular activities build up organic forms, and main¬ 
tain their vital functions. 
No one was more fully alive to this supreme scientific desideratum 
than Darwin himself. He devoted more intense thought to the elabor¬ 
ation of his “provisional hypothesis of Pangenesis”—as he modestly 
calls it—than on that of natural selection. No wonder, for it required a 
gigantic effort of visualizing imagination to make the evolutions of a 
host of separately specific molecules account for the complex of biologi¬ 
cal facts connected with reproduction and heredity. 
This is the way Darwin puts the leading question, he asks: “ How can 
the use or disuse of a particular limb or of the brain affect a small 
aggregate of reproductive cells, seated in a distant part of the body, in 
such a manner that the being developed from these cells inherits the 
characters of either one or both parents?” He adds: “ Nothing in the 
whole circuit of physiology is more wonderful.” “Even an imperfect 
answer to this question would be satisfactory.” 
Let us then see b} 7 " means of what hypothetical devices he himself 
seeks to answer this perplexing question. He takes, above all, for 
granted that the complex organism consists of autonomous units, as 
taught by the cell-theory. And he goes, as he says, one step farther, 
and assumes that these autonomous cell-beings throw off reproductive 
gemmules. 
