SPENCER AND PANGENESIS 25 



us an historical interest because it had much influence upon 

 biological investigation and theory at that time and subse- 

 quently. Logically, Darwin's theory of pangenesis may be 

 regarded as a modification of one of Herbert Spencer's specu- 

 lations upon biology. 



Herbert Spencer (1820-1903) was the champion of evolu- 

 tion from the standpoint of philosophy, as Huxley was from 

 the standpoint of comparative anatomy and embryology. 

 His ideas had much influence on the development of evolu- 

 tionary thought down to our own time. (See Delage and 

 Goldsmith, 1912.) Spencer tried to explain the structure of 

 living substance (protoplasm) in harmony with the chemical 

 explanation of lifeless substance then current. He supposed 

 that there are structural units of protoplasm comparable with 

 the molecules of chemical compounds, each kind of proto- 

 plasm within the body being composed of a different kind or 

 kinds of units. These he called physiological units. 



Darwin adopting this same line of thought, but with a 

 more intimate knowledge of the facts of inheritance, saw that 

 every kind of physiological unit must be supposed to exist in 

 the germ-cell, since out of the germ-cell an entire body de- 

 velops. In his theory of pangenesis, he supposes that every 

 part of the body is constantly giving off its particular kinds 

 of units into the blood, just as a fungus gives off spores into 

 the air. These given off units Darwin called " gemmules," 

 or little buds. He supposed further that these gemmules are 

 carried through the body in the blood stream, and accumu- 

 late in the germ-cells, in which they multiply as the germ-cell 

 develops. Thus out of one germ-cell comes an entire body 

 with its various parts, because each part was represented in 

 the germ by a gemmule. No one today holds this theory, as 

 Darwin stated it, but the underlying idea of preformed deter- 

 mining particles existing in the germ-cell reappears a little 

 later in Weismann's theory of heredity, and has wide accep- 

 tance today in the chromosome theory of inheritance. 



We shall come to these later, but for the present let us go 

 back to Darwin's theory of pangenesis. Darwin's method of 



