Studies on Synapsis. 



77 



flu view that the integral continuity of the chromatinic organisation of the 

 nucleus is interrupted in the diffuse stage. 



The Yolk Nucleus of Libellula. 

 In concluding this record of the history of the ovarian oocyte in L. depressa 

 reference is due to a crescentio body found in a juxtanuclear position in 

 Anax ; this is stated to undergo fragmentation and dispersal in the cyto- 

 plasm of the egg as growth proceeds. McGill calls it the yolk nucleus on 

 the analogy of a similar structure described by Calkins and Foot in the egg 

 of Lumbricus and Allobophora. Such a body is also present in the oocytes 

 of Z. depressa. After the examination of preparations fixed in Flemming's 

 modified formula (without acetic acid), and by the Mann-Kopsch method * 

 followed by turpentine to remove osmicated fat, it appeared that the yolk 

 nucleus is in reality the mitosome or chondriome of the oocyte, being the 

 area in which the mitochondria are congregated. This not infrequently 

 resists injurious fixation in young oocytes — perhaps because the protein 

 component still differentiates from the ground cytoplasm after the lipins 

 have been extracted. Gatenby has described the dispersal of the mito- 

 chondria in the oogenesis of Apanteles recently; and the facts are 

 essentially similar in Libellula, except that in the latter the mitochondria 

 do not appear to become filamentous. An interesting point noticed was 

 that in some cases the spherical bodies emitted from the plasmosome and 

 lying in the periphery of the egg outside the mitochondrial area were 

 sometimes seen to be invested with a cloud of mitochondrial granules 

 (figs. 38, 39). 



The work of Gatenby (17), Hirschler (18) and others has shown quite 

 clearly that both mitochondria and dictyosomes (Golgi rods) may be trans- 

 formed into deutoplasmic spheres. On the other hand, Gatenby and 

 Nusbaum Hilarowicz (19), who has recently demonstrated a Golgi apparatus 

 in Dytiscus eggs, were not able to trace the origin of the yolk in the 

 Hexapod egg to the cytoplasmic inclusions. Is it therefore necessary to 

 conclude that the mechanism of yolk formation with respect to the cell 

 organs is totally different in different animals ? The observation recorded 

 above seems to offer an alternative, Jorgensen's researches, though 

 unfortunately largely vitiated by inadequate technique, do at least show 

 that yolk formation throughout the animal kingdom coincides with a period 

 of intense metabolic activity on the part of the plasmosome ; it is equally 

 certain that the process of yolk formation in general corresponds with a 

 period of rapid increase in number of the extra-nuclear cell elements. Is it 



* Saline corrosive 2^ hours, aq. dest., osmic acid 2 per cent. 10 days. 



G 2 



