38 GENETICS AND EUGENICS 



dence. But even supposing it to have statistical significance, 

 it may be due, as Sumner suggests, to differences directly 

 impressed upon the germ-cells while they were contained 

 within the body of the parent and the parent itself, being 

 very young, varied in body temperature with the room in 

 which it was born. If so, there can be no question of a 

 transfer of an effect from body to germ-cells, but only of 

 simultaneous modification of the two. 



7. Pressure effects. It is well known that pressure has 

 direct effects upon the parts of the body. The skin on the 

 soles of our feet is thickened where our weight rests upon it, 

 and callouses form on the hand when it is used at hard work. 

 A long illness, during which the person does not stand upon 

 his feet causes the thickenings on the feet in part to disappear. 

 They are undoubtedly due directly to pressure. Yet all pre- 

 vious generations of man have been subjected to the same 

 action, and if acquired effects are inherited this should be. In 

 fact, it is found that in the foetus of man, long before birth 

 (from five months on) the skin is thicker on the sole of the 

 feet than on the back of the foot. If this is not to be regarded 

 as an inherited effect of use (pressure), it will be necessary to 

 explain how the skin came to be thickened originally in those 

 particular regions where use induces thickening. 



The camel's hump has been cited as a character acquired 

 by pressure, carrying loads on its back. But this is a less 

 fortunate example for the Lamarckians, for the camel's hump 

 is not due probably to pressure at all. It represents rather a 

 reserve food organ, like special accumulations of fat in most 

 animals. For not all animals which carry loads on their backs 

 acquire humps, for example the ass, the horse. Further, 

 animals may acquire humps without carrying loads, as the 

 American bison and the humped cattle of India. 



8. Light effects. Kammerer has experimented with the 

 European spotted salamander (" fire salamander ") which is 

 mottled with black and yellow areas. He finds that if sala- 

 manders are kept on a yellow background, the yellow areas 

 become more extensive, while if the animals are kept on a 



