304 EMBRYOLOGY 



has not stated what substance in the cell is actually the idioplasm. 

 A real basis must therefore first be won by empiric investigation. 

 This occurred contemporaneously and independently by Stras- 

 burger and myself; Weismann, Kolliker, and others soon followed. 1 



Proceeding from the facts of karyokinesis, of fertilization and 

 maturation, I concluded that the substance of the nucleus, and here, 

 especially the chromatin, corresponded to the idioplasm of Naegeli. 

 Three important considerations appeared to me to point in this 

 direction. 



First: The chromatin is the only substance known to us which 

 occurs in exactly equal amount in the sperm- and egg-cells. As a 

 proof 1 will recall briefly the already mentioned brilliant discovery 

 of van Beneden, according to which the egg- and sperm-nuclei of 

 Ascaris megalocephala bivalens contain the same number of chromor 

 somes, that is, two, which are of equal size. 



Second: the fact that the chromatin is the only substance which 

 passes over in equal quantity from the mother cell to the daughter 

 cell, after it has doubled its volume by nourishment and growth. 

 The complicated process of karyokinesis evidently serves only for 

 this purpose. The arrangement of the chromatin particles in threads, 

 the division of the chromosomes longitudinally, the distribution 

 of their split halves toward the poles of the spindle, and the equal 

 distribution in the daughter cells. 



Thus, this substance, in which rests the peculiarity of the organ- 

 ism, is carried down from one cell generation to the next as a valu- 

 able inheritance, and thereby is the principle by which every cell 

 of the organism is "idioplasmatically enabled," as Naegeli expresses 

 it, to become the germ of a new individual. Here also numerous 

 phenomena of generation and regeneration find their explanation. 

 For in many plants and lower animals we see that actually almost 

 every small cell complex separated from the rest of the organism 

 is able to reproduce the whole. From the root-cells of a plant, buds 

 may form, to reproduce the aerial part, and from the stem-root, cells 

 may develop, as is seen in slips. This is because, in cells, which 

 during the course of development have adapted themselves for a 

 certain function, the deposits contained in their inherited mass are 

 still slumbering, and may be newly awakened and forced into a 

 definite development. 



Thirdly and finally, we may base our opinion upon the chroma- 

 tin reduction. I might denote this as a proof of the justification of 

 the theory. Without having known of the finer processes which 

 occur during the formation of the polar cells, Naegeli had already 



1 I have given the different historical and critical opinions, in regard to the 

 theory of fertilization and inheritance, in my article Comparison of Egg and 

 Sperm Formation in Nematoda, Arch, fur mikrosk. Anat., vol. xxxvi, pp. 77-127, 

 1890, and in Zeit. und Streitfragen der Biologie, vol. i, p. 16, 1894. 



