266 GENERAL ZOOLOGY 



tions. This idea is the basis of the theory of the continuity of 

 the germ plasm which was developed vigorously by the German 

 zoologist, August Weismann (1834-1914). According to this 

 view, the developmental and hereditary qualities of the germ cells 

 are derived from antecedent germ cells, the somatic cells of each 

 generation serving in a purely vegetative capacity as a means of 

 protection and of supplying the metabolic needs of the germ 

 cells, but contributing nothing to the hereditary qualities of the 

 germ cells. The facts of development support this idea in many 

 cases of animal embryogeny but not in all. 



From the Weismannian point of view, on purely a priori 

 grounds, one should expect that acquired characters (i.e., pecu- 

 liarities acquired by the somatic cells through special training or 

 experience) would not be inherited, because there is no conceiv- 

 able way in which changes in somatic cells, caused by environ- 

 mental factors, could induce changes in the germ cells of such a 

 nature that the latter would reproduce the somatic condition in 

 the absence of the original cause. This does not mean that genes 

 cannot be disturbed by external causes acting directly on the 

 germ cells or indirectly through the somatic cells, but that a 

 specific somatic effect, produced by external causes, does not 

 produce a corresponding hereditary effect. One difficulty in 

 dealing with this question in a limited space is that the term 

 "acquired characters" includes a large category of conditions 

 that are not all comparable. Every one knows that if a man 

 loses his legs as the result of an accident, his children are not born 

 legless. All such mutilations are not inherited. Neither is there 

 any ground for the belief that maternal impressions produce 

 specific effects on the unborn human young. The uterus is a 

 place in which the fertilized egg develops — the kind of individual 

 developing from that egg depends upon the kind of parents that 

 produced it or more accurately upon the kind of ancestral germ 

 cells preceding it. Experimentally it has been impossible to 

 produce an inherited defect following an alteration in the somatic 

 tissue. Observation and experiment over a wide field fail to 

 demonstrate satisfactorily the inheritance of an acquired condi- 

 tion. On the other hand, had no characters been acquired by 

 primitive protoplasm, there would have been no evolution, and 

 consequently no great variety in life. A partial answer to this 

 question is that the hereditary material of the germ cells does 



