i] THEORIES OF HEREDITY 137 



enable him to formulate one of the first really impor- 

 tant theories of heredity, which he called the Theory 

 of Pangenesis [7, (1868)]. The essence of his theory 

 was that every cell of an organism gives off minute 

 particles or ' Gemmules ' from itself, which circulate 

 in the body and finally come to rest in the germ-cells, 

 or in parts where buds may be developed. The 

 gemmules were regarded as being capable of multi- 

 plication, and of transmission to a future generation 

 in a dormant state. They were supposed to be given 

 off from all tissues at every stage of development, so 

 that every unit of the organism at every stage would 

 be represented in the germ-cells. On the develop- 

 ment of the germ-cell, the contained gemmules 

 would give rise to cells like those from which they 

 were derived, and so the characters of one generation 

 would be transmitted to those which follow. 



By this hypothesis Darwin accounted for the 

 phenomena of sexual and non-sexual reproduction, 

 regeneration of lost parts, variability, inheritance 

 both of inborn and acquired characters, and lastly 

 of reversion to a previous ancestor. The hypothesis 

 was one of the first which attempted to bring all 

 these various groups of facts into line, but it had 

 the serious defect that there was no direct evidence 

 whatever for the existence of gemmules, and, assuming 

 their existence, to be accommodated in the germ-cells 

 they must be so exceedingly minute as to be almost 



