1896.] On Heredity and Rejuvenation. 3 



the capacity varies enormously in the different species. In 

 man the power is very small, though more extensive than is 

 generally realized. Among Annelids are species, the individ- 

 uals of which may be divided in two, and each piece can re- 

 generate all that is needed to render it a complete worm. We 

 sometimes see a small fragment of a plant, a single switch of 

 a willow, for instance, regenerate an entire tree, roots, trunk, 

 branches, leaves, flowers, and all. In the last instance a few 

 cells possess a latent formative force, which we recognize by 

 its effects, but cannot explain. We perceive, therefore, that 

 each individual has, as it were, a scheme or plan of its organ- 

 ization to which it strives to conform. As long as it actually 

 does so, the cells perform their routine functions ; but when 

 an injury destroys or removes some portion, then the remain- 

 ing cells strive to conform again to the complete scheme, and 

 to add the missing fragment. The act of regeneration of lost 

 parts strikes the imagination almost as an intelligent pursuit 

 by the tissues of an ideal purpose. 



Our knowledge of the regeneration power has recently re- 

 ceived important extensions through the noteworthy experi- 

 ments of Nussbaum 3 and Gruber, 4 who have demonstrated, in- 

 dependently, the possibility of dividing unicellular animals 

 so that each piece will regenerate the missing parts. In this 

 manner the number of individuals can be artifically multi- 

 plied. For example : Nussbaum divided a well-isolated Oxy- 

 tricha into two equal parts, either transversely or longitudi- 

 nally, and found that the edges of the cut became soon sur- 

 rounded with new cilia. Although some of the substance of 

 the body, or even a nucleus, was lost through the operation yet, 

 by the following day, the two parts converted themselves into 

 complete animals with four nuclei and nucleoli (Nebenlcerne) 

 and the characteristic ciliary apparatus. " The head piece has 

 formed a new hind end ; the right half, a new left half." The 



3 M. Nussbaum, Ueber spontan uml h(,>*t *'■ 7AlU:\l» -/, Sitzungsb. d. nei- 

 derrh. Ges. f. Nat. u. Heilkunde, Bonn, 15, Dez., 1884. 



* A. Gruber, f, ■',. r boiMlirh T> <hn, , >,, ; hnvgnnen, Biol. Centralblatt, Bd. IV, 



