SYNAPSIS IN THE EGG OF THE WHITE RAT 443 



distinguish clearly leptotene, synaptene, pachytene, diplotene, 

 and dictye stages, together wdth more or less complicated transi- 

 tion changes to be mentioned later. These various stages suc- 

 ceed each other with considerable regularity throughout the 

 entire ovary, so that at any one time most of the germ cells are 

 in the same stage of the synaptic process. While it is true 

 that those nuclei least advanced in the general process of change 

 are most likely to be found at the periphery of the ovary, there 

 is an absence of that clear distribution of stages in concentric 

 zones so evident in the cat, rabbit, and man (Winiwarter '00, 

 and Winiwarter and Sainmont '08). Because of these features 

 of the process, the difficulty of determining the sequence of 

 stages has been reduced to a minimum. 



THE LAST OOGONIAL DIVISION AND EARLY PRE-LEPTOTENE 

 CHANGES 



The last oogonial division occurs about seven days before 

 birth. In the ovaries of embryos from female 389 (table, p. 444) 

 there are a large number of division figures together with numer- 

 ous nuclei which have not yet passed through the last oogonial 

 division and also many that belong to the early stages of the 

 oocytes. Some few division figures may still be ftjomd in embryos 

 from female 451-6, at six days before birth. The nuclei of the 

 oogonia in the typical resting condition are spherical. They are 

 approximately equal to or perhaps a little small-er than the lepto- 

 tene nuclei to be described later, and are supplied with a large 

 amount of chromatin in irregular blocks. Often one or more of 

 these blocks is comparatively large and conspicuous, somewhat 

 suggestive of the chromatin nucleoli of the post-synaptic stages, 

 though they never have the definiteness of outline characteristic 

 of these later chromatin bodies. A heavy discontinuous spireme 

 is formed during the prophase of the last oogonial division, and 

 often the nuclei appear slightly oval at this time. The chromatin 

 is very closely massed together during the equatorial plate stage 

 as well as during the anaphase, so that it is extremely difficult 

 to distinguish individual chromosomes. The last oogonial divi- 

 sion may be distinguished from previous ones by the numerous 



