38 DUBLIN 



unite into pairs along their whole length, reducing the number 

 to one half. This is in all regards similar to the description of 

 the same stage given by Van Winiwarter, '02, in his excellent 

 work on the oogenesis of the rabbit and man and that of 

 Schoenfeld, '01, in the spermatogenesis of the ox. 



The strongest corroboration of this main thesis, however, has 

 lately come from the botanists. Very striking is the work of Ros- 

 enberg, '03 and '04, on the chromosomes of the somatic and germ 

 cells of a hybrid between Drosera longifolia and Droscra rotun- 

 difolia. The former of these two species contains 40 chromo- 

 somes in its tissue cells and 20 in its germ cells, while the latter 

 contains but 20 and 10 in its soma and germ cells respectively. 

 In the hybrid, however, while the tissue cells contain 30 chro- 

 mosomes, the germ cells in both sexes contain not 15, as one 

 would expect, but 20. These 20 chromosomes, already pres- 

 ent in their definitive form in the earliest prophases of the first 

 maturation mitosis, are of two types : first, 10 large double 

 structures showing a constriction in the middle ; and second, 10 

 single ones. These are distributed irregularly over the spindle, 

 only the double structures being properly placed in the equator. 

 In the ensuing division, the latter 10 divide and pass to the 

 poles to form the daughter nuclei, sometimes taking with them 

 some of the irregularly placed ones which have not undergone 

 any division. The majority of the single chromosomes, how- 

 ever, are left out in the cytoplasm where, after forming dwarf 

 nuclei they degenerate. In the second division, the chromo- 

 somes split longitudinally and four daughter cells each contain- 

 ing, with but {&\N exceptions, 10 chromosomes is the result. 

 From the above, there is but little doubt of the conclusion 

 drawn by Rosenberg : " Es wird also in den Pollen- und Em- 

 bryo-sackmutterzellen etwa im Synapsisstadium ein von Dro- 

 sera longifolia stammendes Chromosom mit einem Chromosom 

 das von Drosera rotundifolia stammt vereinigt . . . , es konnen 

 hier also nur 10 Chromosomen von Drosera longifolia von 10 

 Chromosomen von Drosera rotundifolia sozusagen gebunden 

 werden. Die i'lbrigen 10 Drosera longifolia Chromosomen 

 finden keinen entsprechenden von Drosera rotundifolia und 



