A DYNAMICAL HYPOTHESIS OF INHERITANCE. 29 



gave us a most ingenious physical hypothesis of the constitu- 

 tion of living matter. This, later on, he modified so as to 

 develop an hypothesis of hereditary transmission. But the 

 micellae that were representative of the germinal matter of a 

 species he isolated in the form of rows or chains of micellae 

 traversing the rest of the living substance of the organism, 

 and called it idioplasm. Here again the germinal matter was 

 conceived as separate from that forming the rest of the body. 

 Mr. Spencer supposed " that sperm-cells and germ-cells are 

 essentially nothing more than vehicles, in which are contained 

 small groups of the physiological units in a fit state for obey- 

 ing their proclivity towards the structural arrangement of the 

 species they belong to." These "physiological units" are 

 neither chemical nor morphological in character, according to 

 Mr. Spencer's system, but it is admitted that their properties 

 and powers must be determined in some way by their own 

 constitution, conditions of aggregation, and relation to the 

 outer world. The views of Nageli and Spencer are akin in 

 certain respects, but they still retain a certain amount of re- 

 semblance to the older ones, namely, those hypotheses which 

 assume that the forces of inheritance are lodged in certain very 

 small corpuscles forming part only of the germ or organism. 

 These hypotheses are also dynamical in nature, and have been 

 worked out with the consciousness, in both cases, that the 

 mechanism of inheritance must also be the one through which 

 metabolism operates. Indeed, these two authors seem to be 

 the first to have distinctly recognized the necessity for such a 

 supposition. 



Later still, with the advent of the discovery that the male 

 nucleus was fused with the female nucleus during sexual re- 

 production, it was assumed that the nuclear contents were the 

 only essential material bearers of those hereditary forces that 

 shape the growing germ into the likeness of the parentage. 

 With the development of this idea the name of Weismann is 

 perhaps most closely associated. He has utilized the facts of 

 development, nuclear cleavage, expulsion of polar bodies, halv- 

 ing and subdivision of chromosomes, etc., as the foundation of 

 his hypothesis of inheritance. Its extreme elaboration is its 



