CHAP. XX 



Heredity 325 



these authors were vague and in some respects entirely 

 erroneous suggestions. The best-known form of this type 

 of theory is Darwin's " provisional hypothesis of pan- 

 genesis " (1868), according to which (a) every cell of the 

 body, not too highly differentiated, throws off characteristic 

 gemmules, which (b) multiply by fission, retaining their 

 peculiarities, and {c) become specially concentrated in the 

 reproductive elements, where (^) in development they grow 

 into cells like those from which they were originally given 

 off. This theory was satisfactory in giving a reasonable 

 explanation of many of the facts of heredity, it was unsatis- 

 factory because it involved many unverified hypotheses. 



The ingenious Jaeger, well known as the introducer of 

 comfortable clothing, sought (1876) to replace the "gem- 

 mules " of which Darwin spoke, by characteristic " scent- 

 stuffs," which he supposed to be collected from the body 

 into the reproductive elements. 



Meanwhile (1872) Francis Galton, our greatest British 

 authority on heredity, had been led by his experiments 

 on the transfusion of blood and by other considerations 

 to the conclusion that " the doctrine of pangenesis, pure 

 and simple, is incorrect." As we shall see, he reached 

 forward to a more satisfactory doctrine, but he still allowed 

 the possibility of a limited pangenesis to account for those 

 cases which suggest that some characters acquired by the 

 parents are " faintly heritable." He admitted that a cell 

 "may throw off a few germs" (z.^. "gemmules") "that 

 find their way into the circulation, and have thereby a 

 chance of occasionally finding their way to the sexual 

 elements, and of becoming naturalised among them." 



W. K. Brooks, a well-known American naturalist, pro- 

 posed in 1883 an important modification of Darwin's theory, 

 especially insisting on the following three suppositions : 

 that it is in unwo?ited and ahwrnml conditions that the cells 

 of the body throw off gemmules ; that the male elements 

 are the special centres of their accumulation ; and that the 

 female cells keep up the general resemblance between 

 offspring and parents. For further modifications and for 

 criticism of the theories of pangenesis, I refer the student 



