6 CALIFORNIA ACADEMY OF SCIENCES. 



gemmules, then, is luiproven, and their supposed mode 

 of origin not in altogether satisfactory accordance with 

 organic analogies. Furthermore, the whole machinery 

 of the scheme of heredity is complicated and hyper- 

 hypothetical. It is difficult to read Darwin's account of 

 reversion, the inheritance of functionally acquired char- 

 acters and the non-inheritance of mutilation, or to fol- 

 low his skillful manipulation of the invisible army of 

 gemmules, without being tempted to exclaim — What 

 cannot be explained, if this be explanation? and to ask 

 whether an honest confession of ignorance, of which we 

 are all so terribly afraid, be not, after all, a more satis- 

 factory position."* 



Haeckel's plastidule theory and Spencer's theory of 

 physiological units do not differ very essentially from 

 Darwin's hypothesis of pangenesis, although Spencer's 

 idea is a much less crude one. He finds that the units 

 of which an organism is composed have the property of 

 arranging themselves in a definite form or sequence, 

 and then proceeds to enquire into the nature of these 

 units. He first shows that they cannot be chemical, for 

 the chemical composition of the various organic bodies 

 which arrange themselves in such diverse shapes is 

 essentially alike in all cases. Neither can morphologi- 

 cal units be accepted as final. The simple cell is the 

 morphological unit, but certain tissues arise directly 

 out of the formative substance without the intervention 

 of a cellular stage. Moreover, certain non-cellular or- 

 ganisms, such as Rhizopods, are capable of transmitting 

 peculiar specific characters. From these exceptions it 

 is evident that this formative power does not reside in 

 cells; and consequently both chemical and morphologi- 

 cal units are disposed of. Spencer then argues for 



* Animal Life and Intelligence, p. 137. 



