OOGENESIS IN THE WHITE MOUSE 295 



(parasynapsis) and end to end (telosynapsis) have been described 

 in different forms; and in some of these same forms, union of any 

 sort has been denied. For example, von Winiwarter and Sain- 

 mont describe a parallel or side by side conjugation of chromatin 

 threads in the cat, and R. Van der Stricht ('11), while accepting 

 the results of these authors on many points, states that he finds 

 no evidence whatever for such an occurrence. 



In the mouse the primitive germ cells, as has been described, 

 pass through in the course of their development, a stage which 

 may be termed synizesis. The contraction is more marked, 

 perhaps, in ovaries whose preservation was not the best, but the 

 condition is present, nevertheless,' in well-fixed material. Prob- 

 ably, therefore, its occurrence here is not to be considered an 

 artifact. 



In the development of the definitive germ cells, however, 

 which are formed after birth, there is not the slightest indication 

 of synizesis. There is no period in the differentiation of these 

 oocytes when there is the least appearance of a contraction of the 

 chromatin (figs. 24 to 46). In the mouse, synapsis does not 

 occur, either in the development of the primitive germ cells, or 

 in the differentiation of the definitive oocytes. In the former, 

 there is no evidence of a union, side by side or end to end, of the 

 chromatin threads. These bands of chromatin exhibit no 

 parallelism whatever until they begin to split lengthwise in what 

 is termed the diplotene stage, rather late in development. In 

 the definitive oocytes there are no definite, well-defined chromatin 

 threads in the whole course of early development, from the cell 

 in the germinal epithelium to the nearly mature oocyte in its 

 Graafian foUicle, and accordingly, there can be no question of a 

 union of chromatin bands at all. 



There can be no doubt about the facts in regard to the absence 

 of synizesis and synapsis in the development of the definitive 

 oocytes in the mouse. A careful search was made of the growing 

 egg-cells in the germinal epithelium of ovaries from birth to 

 sexual maturity for just these stages. At first it was thought 

 that they would be encountered, and their absence was doubted. 

 But further study showed convincingly that these stages were 



