446 BENJAMIN H. PRATT AND J. A. LONG 



the appearance of the Unin filaments. A study of the oldest 

 nuclei alone would hardly lead one to such an inference, but the 

 complete series seems very convincing. Such an elaborate 

 series of transformations intervening between the last oogonial 

 division and the leptotene stage has not been described in the 

 ovary of any other mammal carefully studied, though there is a 

 slight indication of such changes in the cat (Winiwarter '00, and 

 Winiwarter and Sainmont '08). 



CONTRACTION FIGURES 



Immediately preceding the leptotene stage, or possibly coin- 

 cident with the earlier portion of it, there is a clearly defined 

 contraction stage. This occurs about six days before birth. 

 The chromatin-linin is eccentrically arranged in a confused mass 

 closely packed against the nuclear wall (fig. 7). Such figures 

 may be found throughout the entire ovary after either Zenker's 

 or Flemming's fixation, fixation that is evidently good in all other 

 portions of the same tissue. Since these figures are found in all 

 portions of well fixed ovaries, and since there is no constancy 

 whatever in regard to the direction of contraction, it is not pos- 

 sible to agree with Schaffner ('07), Von Hoof ('12) and others, 

 who contend that this so-called contraction stage is an artifact 

 due to poor fixation. It seems rather that this stage is quite as 

 normal as those stages immediately preceding or following it. In 

 these figures it is obvious that the eccentrically placed darkly 

 staining mass is not of the same consistency throughout, but is 

 composed of chromatin blocks, granules, and linin threads. 

 Finely attenuated Unin threads often extend from the chromatin 

 knot to the opposite wall of the nuclear cavity. The whole 

 picture strongly suggests that the complex chromatin-linin 

 network has somehow been concentrated at one side of the 

 nuclear cavity, and that those strands of linin attached to the 

 opposite side of the nucleus have not entirely shared in the 

 process. 



