I40 Animal Life and Intelligence. 



can be made to account for anything that has ever been 

 observed or is ever likely to be observed. It is one of 

 those convenient invisibles that will do anything you 

 desire. The regrowth of a limb shows that the cells con- 

 tained some of the original germ-plasm. A little sampled 

 fragment of hydra has it in abundance. It lurks in the 

 body-wall of the budding polype. It is ever ready at call. 

 It conveniently accounts for atavism, or reversion; for* 

 " the germ-plasm of very remote ancestors can occasionally 

 make itself felt. Even a very minute trace of a specific 

 germ-plasm possesses the definite tendency to build up a 

 certain organism, and will develop this tendency as soon 

 as the nutrition is, for some reason, favoured above that of 

 the other kinds of germ-plasm present in the nucleus." 



In place, then, of the direct continuity of germ-cells as 

 distinct from body-cells, we have here the direct continuity 

 of germ-plasm as opposed to body-plasm. The germ-plasm 

 can give rise to body-plasm to any extent ; the body-plasm 

 can never give rise to germ-plasm. If it seems to do so, 

 this is only because the nuclei of the body-cells contain 

 some germ-plasm in an invisible form. The body-plasm 

 dies ; but the life of the germ-plasm is, under appropriate 

 conditions, indefinitely continuous. 



So far as heredity is concerned, it matters not whether 

 there be a continuity of germ-cells or of germ-plasma. In 

 either case, the essential feature is that body-cells as such 

 cannot give rise to the germ — that the hen cannot produce 

 the egg. On either view, characters acquired by the body 

 cannot be transmitted to the offspring through the ova or 

 sperms. The annexed diagram illustrates how, on the 

 view that the hen produces the egg, dints hammered into 

 the body by the environment will be handed on ; while, on 

 the view that the hen does not produce the egg, the dints 

 of the environment are not transmitted to the offspring. 

 On the hypothesis of continuity, heredity is due to the fact 

 that two similar things under similar conditions will give 

 similar products. The ovum from which the mother is 



* Weismann, " Essays on Heredity," p. 179. 



