654 SUMMARY OF CURRENT RESEARCHES RELATING TO 



clearly defined protoplasm surrounding the central corpuscles. During 

 mitosis the protoplasmic mass gives rise to at least a part or probably 

 the whole of the achromatic figure, and from its sharp definition it merits 

 Meves' term of " idiozom." The idiosome of the ovocyte is completely 

 used up during the course of mitosis, but reappears again in the egg 

 during its growth period, showing, however, then slightly different 

 physical appearances. The exact relation between the earlier and later 

 idiosome could not be determined, but it is probable that the latter 

 originates directly from the former. 



Oogenesis in Mammals.* — Dr. Hans von Winiwarter has made an 

 investigation of the ovary iu. the rabbit and in Homo, which finally 

 resolved itself into the consideration of two points: (1) the develop- 

 ment of the ovum up to the time of the formation of the Graafian 

 follicle ; and (2) the development of the ovary itself during the same 

 period. As to the first point, lie finds that, contrary to the usual opinion 

 that the growth-period of the egg coincides with the period of formation 

 of the Graafian follicle, the most important nuclear changes occur before 

 the foundations of the follicle appear. The primordial oogonia have 

 nuclei of ordinary reticulated structure (jctrotobroch nuclei). These 

 increase by karyokinetic division, and when the divisions cease the 

 nuclei of the resulting ovocytes undergo a complicated series of changes. 

 The reticulum gives rise to a chromatic thread (deutdbrock stage), which 

 at first fills the nuclear cavity (leptotsenic stage), and later forms a 

 central dense mass (synaptsemc stage). At this stage the filaments are 

 clearly double ; but as the chromatic thread spreads itself again through 

 the nuclear sj>aco, this duality disappears, and the thread is single, thick, 

 and moniliform (pachytsenic stage). The duality reappears later in 

 the diplotsenic stage, where the thread breaks up into a number of 

 segments, but is lost as the nucleus finally recovers the reticulated 

 condition. In other words, in the interval which separates two 

 reticulated stages, the nucleus exhibits a filamentous condition, the 

 filament becomes double, then single, and finally appears double a 

 second time. As to the meaning of the process, the author is disposed 

 to regard it as follows. Jn the synaptaBnic stage the duality is produced 

 not by division but by the approach of distinct filaments towards one 

 another. The thick moniliform filaments of the pachytaenic stage arc 

 produced by the union of these filaments, and the apparent duality of 

 the diplotaenic stage is produced merely by a loosening of the connection 

 between the previously united filaments. Generally, the author is of 

 opinion that the double appearance of the chromatin thread is an indi- 

 cation of the union of parts, not of the splitting of a previously uniform 

 structure. These results are compared with those obtained by Moon? 

 and Montgomery for other animals, both as to male and female genital 

 products. With Montgomery's results the author's show close analogy, 

 but two striking differences arc apparent. In the cases studied by 

 Montgomery the series of changes ("early anaphase," "synapsis,'' 

 " post-synapsis," " telophase," "i»est-stage "), occur in nuclei which have 

 just divided — in the author's case in resting nuclei. Secondly, the 

 chromosomes in Montgomery's cases remain distinct throughout — in the 

 author's case the chromatic filament is certainly single at the beginning 



* Arch. Biol., xvii. (1900) pp. 33-109 (2 pie. and 2 figs.). 



