240 BIOLOGY; GENERAL AND MEDICAL 



ments of the organism and of having made them the 

 basis of a theory of heredity." 



Darwin 1 formulated a theory of inheritance which he 

 at first imagined to correspond fairly well with Spencer's, 

 though important differences were subsequently pointed 

 out. This theory he calls pangenesis and explains as 

 follows: 



"It is universally admitted that the cells or units of the body 

 increase by self-division or proliferation, retaining the same nature, 

 and that they ultimately become converted into various tissues 

 and substances of the body. But besides this means of increase I 

 assume that the units throw off minute granules which are dispersed 

 throughout the whole system; that these, when supplied with 

 proper nutriment, multiply by self-division, and are ultimately 

 developed into units like those from which they were originally 

 derived. These granules may be called gemmules. They are 

 collected from all parts of the system to constitute the sexual 

 elements, and their development in the next generation forms a 

 new being; but they are likewise capable of transmission in a dor- 

 mant state to future generations and may then be developed. 

 Their development depends upon their union with other partially 

 developed or nascent cells which precede them in the regular 

 course of growth. . . . Gemmules are supposed to be thrown 

 off by every unit, not only during the adult state, but during each 

 stage of development of every organism, but not necessarily during 

 the continued existence of the same unit. Lastly, I assume that 

 the gemmules in their dormant state have a mutual affinity for 

 one another, leading to their aggregation into buds or into the 

 sexual elements. Hence it is not the reproductive organs or buds 

 which generate into new organisms, but the units of which each 

 individual is composed. These assumptions constitute the 

 provisional hypothesis which I have called pangenesis." 



After a lengthy application of the theory to the facts 

 to be explained, he concludes as follows: 



"The hypothesis of pangenesis, as applied to the several great 

 classes of facts just discussed, no doubt is extremely complex, but 

 so are the facts. The chief assumption is that all the units of the 

 body, besides having the universally admitted power of growing 

 by self-division, throw off minute gemmules which are dispersed 

 throughout the system. Nor can this assumption be considered 

 too bold, for we know from the cases of graft-hybridization that 

 formative matter of some kind is present in the tissues of plants, 

 which is capable of combining with that included in another 

 individual, and of producing every unit of the whole organism. 

 But we have further to assume that the gemmules grow, multiply, 



i"The Variation of Animals and Plants under Domestication," 1868, II, 

 Chapter XXVII, p. 349. 



