1887] The Significance of Sex. 157 
prevented, as in male and female parthenogenesis, the resulting 
organisms are weak, we must conclude that the organism derives 
some benefit from the mixture of chromatins that are slightly dif- 
ferent. In the case assumed above, where cell-division is not ac- 
companied by fusion of the nuclei, we may presume that conju- 
gation of gametes supplies this lack,’ though in Opalina the only 
form of fertilization as yet discovered is that of nuclear fusion 
during encystment. But Opalina is a parasite, and parasites, we 
know, get along remarkably well without fertilization. 
This explanation of karyokinesis seems quite plausible, so that 
we may formulate the law ¢hat every cell-division ts preceded by 
fertilization phenomena: ts accompanied by close inbreeding. Other 
explanations have been suggested. Strasburger regards karyo- 
kinesis as resulting in like cells, therefore the different chroma- 
tins present must be carefully divided, so that each daughter-cell 
shall receive its proper ingredients. Roux and Weismann go 
further and call attention to the fact that dividing cells are not 
alike, so that we need a particular distribution of the gemmules 
for each division, so that, to follow the last author, in the first 
egg-segmentation, the histogenic plasm is separated from the 
generative plasm. Thus the soma is descended from one blasto- 
mere and the generative cells from another. In a similar way the 
endoderm-cells have a common ancestor, and the ectoderm 
another, and so on. This explanation seems to me difficult of 
application to the Protozoa, so that the law enunciated above 
- appears to be unaffected. 
3. General—It would extend the length of this paper unduly, 
as well as be of no interest except to the specialist, to discuss the 
various views that have been advanced in interpretation of the 
special stages of karyokinesis. Nevertheless, some of the more 
prominent features should be noticed. We have already seen 
that cell-division need not be necessarily associated with nuclear 
division, whether this be direct or indirect, so in the higher tis- 
sues there occur cells that present such conditions. These are 
the internodal cells of Chara, many fungi where the nuclei are 
granules, and the generative tissues of both plants and animals; 
also in cartilage-cells and marrow-cells. In the generative tissues 
of plants cell-division does not take place until many endosperm 
* The formation of varieties and species must take place in spite of this tendency 
of differentiated chromatins to fm. 
