May, 1906.] A Reducing Division in Ascaris. 523 



tetrads arise by a conjugation of two longitudinally divided 

 chromosomes, one of these maturation divisions is transverse 

 and qualitive representing a true Reducing Division in Weis- 

 man's sense. There next arises the question as to which of the 

 two divisions is the Reducing Division. This point the writer 

 does not hesitate to say is very difficult, or perhaps incapable of 

 complete demonstration in Ascaris. It has seemed to him that 

 the presence of the Reducing Division was the all important fact 

 and that the matter of deciding which division was qualitative 

 was of much less importance. Because of this and because of 

 the great difficulty of the matter I have not tried seriously to de- 

 termine the question in the present investigation. The different 

 chromatids in the tetrads are so similar and so difficult to find 

 in favorable positions where all four of them can be seen at once 

 that it is only with great reserve that statements as to the iden- 

 tity and origin of the separate dyads of the first division can be 

 made. But in this matter the angle between the tetrads may 

 give a clue, not, however, in my judgment amounting to proof. 

 By inspecting such stages a figs. 9 and 10 it will be seen that if 

 we take the nearest common plane of the two tetrads, that in 

 which the angle between them would lie, were it a plane angle 

 (the plane of the paper in the cases cited) then we find that the 

 equivalent chromatids arising by a split, lie perpendicular to that 

 plane and the dissimilar chromatids arising by a transverse break 

 lie parallel to that plane. Applying this to fig. 12 in which the 

 tetrads are oriented for the first division but not yet drawn out 

 of their original angle we find that the first division would be the 

 qualitative for it is the dissimilar dyads which lie on the different 

 sides of the eauatorial plate of the spindle and will pass to the 

 different cells in mitosis. 



The results given above were arrived at after examination 

 of many hundreds of nuclei in the critical stages. The ones se- 

 lected for the figures are unusual only in their clearness and in the 

 favorable position of the parts. Of all the nuclei seen about 

 half were so strongly contracted as to be impossible of resolution. 

 Of the others all but two or three were clearly interpretable as 

 stages in the process outhned above. A few, about 1-3 

 per cent, should be interpreted either as products of folding or 

 of a double longitudinal division. None were found which could 

 be interpreted as products of the latter process which did not 

 lend themselves equally well to the other interpretation. 



Inasmuch as the results of the present investigation are 

 diametrically opposed to those reached by Brauer (2) on the sper- 

 matogenesis of the same object, it might seem difficult to bring 

 the observations of Brauer into harmony with those of the pre- 

 sent writer. But such is not at all the case. One point which 

 Brauer lays great stress upon and which is at first sight most con- 

 vmcmg, is that the granules are sometimes clearly doubly split 

 at a very early period. Whatever the significance of this group- 



