CHROMOSOMES IN THE SPERMATOGENESIS OF THE HEMII'TERA HETEROPTERA. 147 



question that they fulfill an important part in the interplay of nuclear and cyto- 

 plasmic activity, an influence perhaps in proportion to their size. Yet this influence 

 can hardly be one of the nature of an assimilation process, else the chemical nature of 

 the two allosomes could not remain so constant during the growth period. 



2. The Nuclear Element and Chromosomal Difference. 



More than twenty years ago r'arnoy (1885) spoke of the Metazoan nucleus as con- 

 taining an "element nucleinien," by which he meant a continuous complex of linin 

 and chromatin. We now know that his idea of nuclear structure was not exact, that, 

 for instance, in the majority of nuclei there is no well marked chromatin spirem 

 through the rest stage of the cell as he conceived it. Yet Carnoy had probably the 

 right general idea. In my analysis of the spermatogenesis of Peripatus (1900), which 

 was quite largely an examination of the changes of the linin threads, I went into con- 

 siderable detail into the connection of the chromatin and the linin, and developed the 

 thought very similar to that of Carnoy, that as the nuclear element of the first order 

 should be considered the totality of the linin and chromatin. I conceived of this as a 

 continuous and persisting linin band with which the chromatin masses are always in 

 contact. The unity of this element is best seen in the prophases of cell division, where 

 there is a continuous linin spirem with chromatin masses segregated upon it. But 

 though the linin band becomes very much branched in the rest stage, and the chro- 

 matin particles become finely distributed along these branches, yet there is consider- 

 able evidence that it always maintains its continuity as a single band. In all sperma- 

 togonic divisions the whole band, not only the chromatin masses, probably divides 

 along its entire length, so that each daughter nucleus would receive one half of the 

 original nuclear element ; but in the reduction division this band would become 

 transversely divided, therefore broken into as many portions as there are chromosomes. 

 And I showed (1900, 1901?^) that just after the reduction division, and in the earliest 

 cleavages of the fertilized egg, the chromosomes are most distinct, presenting the 

 appearance of small, independent vesicles. Therefore the reduction division causes 

 the segmentation of the nuclear element, and accordingly it must become reconstituted 

 before the spermatocyte and ovocyte stages of the next generation. All this is in 

 accord with the phenomenon of the paternal and maternal chromosomes forming 

 separate groups in the spindle in only the earlier embryonic cleavages, and not, as 

 Hacker has argued, through the whole germinal cycle. 



This was all elaborated at length in the earlier papers of mine referred to, and 

 there shown to explain the mechanics of very diverse cellular changes. To that I 

 would now add another thought. When the nuclear element becomes segmented by the 



