106 FOOT-NOTES TO EVOLUTION. 
the germinal protoplasm, and that, therefore, develop- 
ment is, in the words of Professor Whitman, “a function 
of organization.” 
Inheritance and variation are general terms which 
include a great many different kinds of phenomena, 
many of which seem to be due to entirely different fac- 
tors. A great many phenomena of inheritance seem to 
be due entirely to extrinsic forces, but a more.careful 
inquiry always reveals the fact that they are invariably 
due to the reaction of certain extrinsic causes on a per- 
fectly definite living structure. As examples may be 
mentioned the following: 
(2) The tiger-like striping of the egg of Fundulus, 
which is very characteristic and would certainly be re- 
garded as an inherited character, has been shown by 
Loeb * to be due entirely to the position of the blood 
vessels of the blastoderm. The pigment cells are at first 
uniformly distributed, but when the blood vessels are 
formed they gather around them, probably through 
chemotropic action, and thus the characteristic banded 
appearance is produced. Graft has since shown that 
the colour patterns of ,leeches are produced in the same 
way. It is not necessary, therefore, to assume that the 
colour patterns in these cases are specifically represented 
in the germinal protoplasm; it may even be that the 
position of the blood vessels is not so represented, but 
there must be some ultimate cause back in the germinal 
plasm itself which determines the series of causes which 
finally produces the colour patterns, In short, this fea- 
ture, like most others, was predetermined from the be- 
ginning. 
* Jacques Loeb. Some Facts and Principles of Physiological 
Morphology. Biological Lectures, 1893. 
+ Arnold Graf. Ueber den Ursprung des Pigments und der 
Zeichnung bei den Hirudineen. Zool. Anzciger, No, 468, 1895. 
