28 BIOLOGICAL SOCIETY OF WASHINGTON. 



and may actually constitute the leading property of the high 

 est organic compound protoplasm, and I venture to suggest 

 here that the gemmules of Darwin and the physiological 

 units of Spencer may be nothing more than the molecules of 

 protoplasm, which, as I have explained, are so immensely 

 complex that any required degree of difference in their essen 

 tial constitution may easily exist. 



The only other theory of heredity which time will warrant 

 my mentioning now is that of Professor Haeckel, published in 

 1876 and known as "the perigenesis of the plastidule." To 

 avoid the possibility of misstatement, I will give this theory 

 in the words of its author, as epitomized in the latest (8th) 

 edition (1889) of his Schopfungsgeschichte (pp. 200-201): 

 "The perigenesis-theory was founded by me in 1876 in a 

 memoir ' on the wave-reproduction of vital particles or the 

 perigenesis of plastidules,' and as a 'provisional attempt at a 

 mechanical explanation of the elementary processes of devel 

 opment,' and especially of heredity. (In the second part of 

 my collection of popular lectures, Bonn, 1879, pp. 25-80). The 

 perigenesis-hypothesis seeks to explain heredity by a simple 

 mechanical principle, namely, by the well-known principle of 

 transmitted motion. I assume that in every process of repro 

 duction not only is the special chemical composition of the 

 plasson or plasma transmitted from the parent to the offspring, 

 but also the special form of molecular motion which belongs 

 to its physico-chemical nature. In harmony with the funda 

 mental laws of modern histology and histogeny, I assume that 

 this plasma (either the caryo-plasma of the cell-nucleus or the 

 cytoplasma of the cell-body) is alone the original bearer of 

 all vital activity, and hence also of heredity and reproduction. 

 In all plastids (as well the anucleated cytodes as the genuine 

 nucleated cells) this plasma or plasson is composed of plasti- 



