1895.] ^^ [Coiikliu. 



increase in size as soon as more abundant food is provided, and tliis 

 takes place by the active growtli and division of all the cells of the 

 body. In higher animals, once maturity has been reached, there is 

 little chance for groAvth, apparently because many of the cells are so 

 highly ditferentiated 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 differentiated and 

 are capable of division, it follows that Ihey Avould not be permanently 

 modified by starving. It may be, as Prof. 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 very slight as compared with the cumulative effects of selec- 

 tion in breeding, and it is safe to assert that there is no such wholesale 

 and immediate modification of the germinal plasm due to the influence 

 of nutrition as some people seem to suppose. 



(2) The interesting experiments of Schmankewitsch in transforming 

 one species of Artemia into another by gradually increasing the salinity 

 of the water, or in transforming Artemia into another genus, Branchi- 

 necta, by decreasing the salinity of the water are Avell known, and are 

 often cited as illustrations of the fact that specific and even generic 

 differences may suddenly be produced under the influence of the 

 environment. The very fact, however, that these changes are sud- 

 denly produced, and that they can at will be quickly modified in one 

 direction or the other is evidence that they are not represented in the 

 structure of the germinal plasm, and the fact that definite extrinsic 

 causes, sucl^is salt or fresh water, acting upon this plasm produces 

 results which are constantly the same is the best evidence that the 

 internal mechanism, i. e., the structure of the germinal plasm, is con- 

 stantly the same. The same can be said of many artificially produced 

 modifications, such as the exogastrulas and potassium lai-vse of Herbst, 

 all of which profound changes are due entirely to extrinsic and not to 

 intrinsic causes, as is shown by the fact that they disappear as soon as 

 the immediate extrinsic cause is withdrawn. The same thing is shown 

 in Poulton's experiments on the colors of Lepidopterous larva;, and in 

 this case also it is known that the changes are not inherited, at least 

 during the limited period through which the experiments were con- 

 ducted ; and it should be observed that to assume that this would take 

 place at the end of an indefinite number of generations is simply to beg 

 the question. 



Very many other cases of a similar character might be instanced 

 under this head if time permitted, but I hasten on to another class of 

 evidence. 



Under the subject of the inherited effects of use and disuse the fol- 

 lowing cases may be mentioned as showing how inconclusive much of 

 this evidence is : 



