1892.] NATURAL SCIENCES OF PHILADELPHIA. 465 



pounded by H. Milne Edwards, that all the plasma, or the whole of 

 the specific protoplasm or idioplasm of the orgaiiism, becomes physio- 

 logically differentiated and incajxihle of undergoing embryonic develop- 

 ment, excejA that of the germ-cells or germinal plasma, as long ago 

 urged by Professor Huxley, we get the same result as that reached 

 by Weismanu without involving ourselves in the consequences 

 which beset his hypothesis. This germinal matter is the only func- 

 tionless and idle plasma in the parent body, capable of growing and 

 consequently of multiplying its substance within the parental 

 organism at the expense of the surplus metabolism of the latter as 

 a whole. Moreover, the germinal cells are alone capable of detach- 

 ing themselves, or being detached, from the parental organism as 

 products of over-nutrition, which have become useless to the life of 

 the parent, as assumed in my preliminary paper "On the origin 

 and meaniug of sex." This recognizes the apparent fact of the 

 setting aside or isolation of the germ-plasma, but does not make 

 that fact the cause of the stability of species through the continuity 

 of processes of growth, and the assumed but not empirically demon- 

 strated isolation of such germ-plasma. My interpretation is in 

 absolute accord with the requirements of the principles of modern 

 physiology, while the hypothesis of Weismann and his followers is 

 in conflict with those principles, and ultimately, as a necessary conse- 

 quence, with the still more comprehensive principle of the conserva- 

 tion of energy. Modern physiology, as well as the doctrine of the 

 conservation of energy, positively forbids us to interpose any bar- 

 rier between the plasma of the parent-bod}^ and that of the germ cells, 

 as is done by the promulgators of the hypothesis of the continuity 

 and isolation of the germ-plasma. To do so robs us of the possibil- 

 ity of appealing to the agency of the workings of metabolism as the 

 efficient cause of the modification of the germinal matter. Since 

 metabolism, and all that it implies, is the only agent to which, 

 according to modern physiology, we can appeal, without interjecting 

 gemmules, plastidules, pangens or some other accessory and needless 

 agency into living organisms, as the efficient agents in the transmis- 

 sion of hereditary traits, we are restricted in our choice to metabol- 

 ism alone. In this way only is it possible to get rid of a deus ex 

 machina in the form of an idioplasm in the sense first implied by 

 Niigeli, or of the gemmules of Darwin and Brooks, the plastidules 

 of Haeckel, the pangens of De Vries, or the physiological units of 

 H. Spencer. 



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