INHERITANCE OF ACQUIRED CHARACTERS 201 



imperfect. However, in a flounder reared under conditions in 

 which the light falls on the lower side, pigment cells are de- 

 veloped also on that side. 



It has been claimed by certain writers, as Cunningham, that 

 the twisting of the head in the flounder is due to the inheritance 

 of an acquired character. A flat fish without air bladder, rest- 

 ing on the sea bottom, naturally falls on one side. The eye 

 thrust into the sand is naturally twisted around to the upper 

 side, and this tendency begun in very young individuals becomes 

 hereditary, while the lack of pigment on the under side is also 

 transmitted by inheritance. But it is just as easy to claim 

 that the first trait of adaptation is due to natural selection, and 

 that the whiteness of the blind side is ontogenetic, due to the 

 absence of light in the growth of the individual. In any case, no 

 specific theory of the origin of the twist of the flounder's head 

 can be regarded as proved. 



It is well known, as Dr. Conklin observes, that certain water 

 snails "if reared in small vessels are smaller than when grown 

 in large ones," and this case has been cited as showing the 

 influence of environment in modifying species. There is good 

 evidence, however, that this modification does not affect the 

 germinal protoplasm, for these same gasteropods will grow 

 larger if placed in larger vessels. It seems very probable that 

 the diminished size of these animals is due to deficient food 

 supply, but this has so little modified the somatic protoplasm 

 that, although they may be fully developed as shown by sexual 

 maturity, they at once increase in size as soon as more abundant 

 food is provided, and this takes place by the active growth and 

 division of all the cells of the body. In higher animals, once 

 maturity has been reached, there is little chance for growth, 

 apparently because many of the cells are so highly differen- 

 tiated that they can no longer divide; consequently the growth 

 is limited, and hence the size of the adult may depend in part 

 upon the amount of nutriment furnished to the embryo. This 

 limitation of growth is due to the high degree of differentiation 

 of the somatic cells. But as the germ cells are not highly dif- 

 ferentiated and are capable of division, it follows that they 

 would not be permanently modified by starving. It may be, 

 as Professor Brewer argues, that long-continued starving and 

 consequent dwarfing of animals may leave its mark on the 

 germinal plasm; but, as he also remarks, this influence must be 



