Relation Betiveen Germ Cells and Environment. 249 



sembles the movements of pigment cells, and suggests the col- 

 lecting of leucocytes toward points of infection. While most 

 of the somatic cells of the embryo are syncitial during these 

 early stages, the germ cells show sharp contours, and by their 

 migration they must certainly break any protoplasmic bridges 

 that may have united them with surrounding cells. It is, how- 

 ever, quite possible that new protoplasmic bridges may be 

 afterward established. Color is lent to such a view by the re- 

 lation of the follicular cells to the ovum in many vertebrates. 

 Whether this be true, or not, there are intimate chemical re- 

 lations between the germ cells and the soma. 



The rapidly multiplying male germ cells, and the ova, with 

 their enormous increase in size, demand large amounts of nu- 

 triment. Various other substances in the blood are absorbed 

 into these cells, as demonstrated by Riddle in his experiments 

 of feeding Sudan III to hens. If we assume that slight changes 

 in the chemical constitution of the germ plasm might modify 

 its hereditary tendencies, then it would be easy to understand 

 that many changes in the substances carried by the blood, such 

 as foods, drugs, waste products, internal secretions, etc., must 

 exert a decided influence, because we should expect them to 

 modify so complex and unstable a substance as protoplasm. 



Unfortunately, we know but little regarding the nature of 

 the changes that these substances may produce in the germ 

 plasm. 



These are the a prioii, considerations. What are the facts? 



Certain external influences are found to produce deleteri- 

 ous eff"ects upon the germ cells. Bardeen subjected the germ 

 cells of toads to the action of X-rays, and found that while the 

 fertilized egg started to develop, the embryos produced became 

 more and more abnormal. Similar effects have been produced 

 by radium. 



Stockards' experiments upon alcoholized guinea-pigs show 

 that poisons not only affect the soma but the germ cells as well, 

 and that the injuries are manifested in later generations in 

 weakened, defective individuals. 



These effects are of a gross general nature and do not touch 

 the question of the more subtle changes that may be produced 

 in the germ cells by the action of external influences. 



The striking experiments of Tower upon Leptinotarsa, of 

 Klebs upon Sempervium, of MacDougal upon Oenothera and 



