Jax. 1902.] BOTANICAL SOCIETY OF EDIXBUKGH 153 



future sex is betrayed by the nature of the egg itself. It 

 is announced by difierentiation of ovary or testis. 



So far as the germ-cells themselves are concerned, the 

 duplication of the paternal and maternal nuclear portions is 

 one of no long duration; for a commencement of the undoing 

 of it is made at the formation of the secondary geim-cells. 

 That is to say, the doubling brought about by the conjugation 

 only persists until the primary germ-cells cease to be such, 

 and divide to form secondary ones. Moreover, the tendency 

 of research goes to demonstrate a certain looseness in this 

 union. As Eueckert and Haecker independently showed 

 a few years ago, the paternal and maternal chromosomes 

 remain distinct during the cleavage of Cyclops, indeed, in 

 such a manner as to suggest a duplex-nucleus in each of 

 th6 cells along the germinal track (in Weismann's sense).^ 

 The like observation was subsequently made by the former 

 in the cleavage-cells of Torpedo, without, however, suggest- 

 ing any connection with germ-cells. The same duplication 

 was recently noted by the writer in cleavage-cells of Raja, 

 as well as in the primary germ-cells here, and the two were 

 brought into connection. The interesting point about the 

 matter appears to the writer to be that, if the reduction of 

 chromosomes at the determination of sex for the following 

 generation be ever a mere undoing of the previous lax 

 union, the resulting germ-cells may reproduce or mimic 

 more or less exactly, if not, indeed, absolutely so, the 

 corresponding germ-cells of a grandparent. After such a 

 reduction and new conjugation the reduced lialves of the 

 nuclei have, of course, lost the previous loose union referred 

 to above, in order to acquire a new one of the like nature. 

 Therefore they cannot so easily revert to a great-grand- 



1 The WOP' I " epigenesis " is here deliberately avDided. After very 

 prolonged study of the mode of vertebrate developinenr, my conclusion 

 is, that epji^enesis has no existence. In the jjreface to his "Germ- 

 plasm," Weismann writes : "I finally became convinced that an epigenetic 

 development is an impossibility. Moreover, I found an actual proof 

 of the reality of evolution," etc. Though there be no preformation, 

 there is a p'r. destination ; and this is finally lirou<^ht to pass by an 

 evolution or unfolding. In my own work the facts of the development 

 of the thymus, ot the lateralsense organs, of tlie whole gut, etc., are 

 only explicable and intelligible on this view. Evidence of the like 

 kind is also afi"iirded by the facts as to the developmental origin of like- 

 twins. The very instance, chosen by Caspar Fried rich Wolff, that of 

 the development of the alimentary canal, in realit\ demonstrates in the 

 •clearest fa.shion that its history is one of an evolution. The detailed 

 facts coucerniiig this may be brought forward! on an early (jccasion. 



TRAXS. BOT. SOC. EDIX. VOL. XXII. L 



