1896.] On Heredity and Rejuvenation. 5 



not go much beyond the proof of existence, to a high degree, 

 of the regenerative capacity in unicellular organisms, He also 

 makes the significant observation that in the Protozoa, we 

 have to do foremost with changes of function ; in the Metazoa, 

 with growth also. 



2. Duplication of parts. — In these anomalies we find an or- 

 gan which, although an extra member, yet still conforms to 

 the type of the species. For example : a frog is found with 

 three posterior limbs ; dissection proves the third leg to agree 

 anatomically with the typical organization of the frog's hind 

 leg. In determining the importance to be attributed to this 

 evidence, it should be remembered, on the one hand, that 

 these instances are by no means unusual ; on the other, that 

 the agreement with the normal structure is not uniform. 



3. Asexual reproduction. — When a species multiplies by fis- 

 sion of any kind, we must assume that each part, after divis- 

 ion, possesses the formative tendency, since we see it build up 

 what is necessary so complete the typical organization of the 

 individual. Again : a bud of a hydroid or polyzoon, although 

 comprising only a small part of the body, is equally endowed 

 with this uncomprehended faculty. In pseudova we reach the 

 extreme limit ; in aphis, for example, the parent gives off a 

 single cell, the capacity of which, to produce a perfect and 

 complicated individual, fully equals the like capacity of a hy- 

 droid bud or of half a worm. 



The evidence forces us to the conclusion that the formative 

 force or cause is not merely the original disposition of the 

 forces and substances of the ovum, but that to each portion of 

 the organism is given : 1. The pattern of the whole organism; 2. 

 The partial or complete power to reproduce the pattern. The itali- 

 cized formula is, of course, a very crude scientific statement, but 

 it is the best which has occurred to me. The formative force, 

 then, is a diffused tendency. The very vagueness of the ex- 

 pression serves to emphasize our ignorance concerning the 

 real nature of the force. In this connection, I venture to in- 

 sist upon the fact that we know little or nothing concerning 

 any of the fundamental properties of life, because I think the 



