266 The American Naturalist [April, 



The origin of the heredity cells may be explained in one of 

 three ways : 2 



I. The sex cell is the product of the whole organism, and is 

 in this apart from the other tissues. This is the Pangenesis of 

 Darwin. 



II. The sex cell is an unchanged but increased part of the 

 sex cell of the previous generation, and something apart from 

 the rest of the body. This is Jaefferism, or, more popularly, 



Weimwnnism, and, according to it, the body has no influence 

 over the hereditary cells and changes arising during the life of 

 one individual cannot be transmitted to the next generation. 



III. The sex cell is the product of histogenesis and of pre- 

 cisely the same significance and origin as any other cell in the 

 body. This view is held by Morgan, Minot and myself. 



As a corollary of the last two is the fact that " in the 

 ancestry of the individual cells of which our body is composed 

 there has never been a death." 



The first two theories are not based on observation. They 

 have been evolved from the attempts to explain the heredity 

 power of the sex cells. 



The idea of the cellular continuity of successive generations 

 first suggested by Nussbaum in 1880, is now generally accepted. 

 Indeed, there is, perhaps, now no one who would contend that 

 the reproductive cells are new formations in the individual. 

 The reproductive cells are known to be of the same origin as 

 the retinal or any other series of cells. There is but little less 

 unanimity over the idea of the continuity of the unchanged 

 germ plasm, although the number of observations bearing on 

 this point have, necessarily, been very limited. 3 So often is 

 the idea restated without actual examination of the data, the 

 whole subject has become hackneyed. I have taken up this 

 subject because it seems to me the conditions observed in Cy- 

 matogaster warrant a conclusion differing from the one gener- 

 ally accepted. 



2 SeeOsborn, Am. Nat., 1892. Morgan, Animal Life and Intelligence, 1891, 

 p. 131. 



5 Boveri, Befruchtung in Ergebnisse der Anatomie und Entwicklungsgesch, I, 

 1892, records an apparent case of unchanged transmission. 



