550 



the resting condition of the nucleus between the two, 

 and exists simply as a rearrangement of the parts. 



From Brauer's work it seems that the so-called "reduction" in 

 the spermatogenesis of Ascaris, is brought about during an inter- 

 vening rest between the last mitoses, just as in the case of the Mam- 

 malia; and we now have it also in the cartilaginous fish — so that 

 it follows that in these widely separated groups, the two last divisions 

 of the spermatogenesis do not correspond to the successive extrusions 

 of the polar bodies; because, between the two mitoses which bring 

 about this extrusion there is n o rest phase, and the supposed absence 

 of this, between the last divisions of the spermatogenesis, was the 

 very fact from which Hertwig argued their similarity! 



Moreover, Boveri seems conclusively to show that there is no 

 "reduction" accomplished in any division up to the formation of the 

 first ovicyte, Dor yet in either division by which the polar bodies them- 

 selves are formed. Yet there are only half as many chromosomes in 

 the divisions which form the polar bodies, as there are in the mitosis 

 prior to the formation of the first ovicyte; and so, ab infra, the 

 reduction must occur in the rest after the division which forms this cell. 



If a comparison can be made at all, the spermatogenesis of the 

 forms under discussion stops short at a point corresponding to the 

 formation of the first ovicyte in the ovigenesis. 



At the present time the study of cellular constituents other than 

 the nucleus must of necessity be chiefly topographical ; but that these 

 bodies will eventually attain a high significance few Cytologists I think, 

 will doubt. When once we have measured the marvel ous diversity 

 of forms which even the same constituent from time to time assumes, 

 it will be possible to deal with these bodies as we deal with the better 

 known structures in cellular anatomy. 



In the cells of which I have been speaking, prior to the two last 

 divisions, there is the usual archoplasmic body enclosing the centro- 

 somes within its substance as two bright staining particles (figs. x). 

 The approach of the penultimate division is shown by the divarication 

 of these centrosomes, which form an extra-nuclear spindle, becoming 

 secondarily related to the chromosomes in the manner described by 

 Hermann in the spermatocytes of Salamaudra 1 ), while this extra- 

 nu clear and intra-archoplasmic position of the centrosomes is here 



1) Arch. f. mikr. Anat., Bd. 37, p. 569. 



Cf. also my description of the origin of the spindle in the sperma- 

 togenesis of Mammals — Internat. Monatsschr. f. Anat. u. Phys., Bd. 11, 

 p. 130. 



