274 H. M. KTNGERY 



made up of granules strung together (figs. 18, 19). At first a 

 fairly regular arrangement as loops is seen in some of the cells, 

 a persistence of the disposition in the preceding stage. This 

 definite arrangement of the chromatin threads, if indeed it be 

 of constant occurrence, is soon lost, and with the further shorten- 

 ing and thickening of the bands, they become irregularly ar- 

 ranged in the nucleus. At least one nucleolus is visible, at 

 first among the ends of the chromatin threads and later almost 

 anywhere in the nucleus. I was unable to distinguish an idio- 

 some at this stage, but the mitochondrial granules, sometimes 

 with a few rods among them, have begun to accumulate in the 

 still rather scant cytoplasm at one side of the nucleus, forming 

 a well-marked crescent-shaped mass. Later, when theidiosome 

 is clearly distinguishable, it occurs in the center of this group of 

 mitochondria, so it is safe to assume that this crescent marks 

 its location. When a definite arrangement of the chromatin 

 threads can be made out, their ends are directed toward this 

 accumulation of mitochondria. 



This pachytene stage is of rather long duration — in fact, cells 

 in this phase are found in the ovary up to a couple of days after 

 birth. It passes into the 'diplotene' stage of von Winiwarter. 

 That is, some of the thick monliform threads of chromatin begin 

 to spht longitudinally (fig. 20). Y-shaped and ring-shaped 

 chromatin segments are formed as a result, depending on whether 

 the bands split at one end first or in the middle. In threads 

 split at one end, the arms of the Y occasionally become twisted 

 around each other, in the 'chiasmatypie' of Jansens, to which 

 some have attached such importance in the explanation of the 

 behavior of certain characters in inheritance — in 'crossing 

 over,' for example. One or two nucleoli are visible during this 

 stage, which is relatively short and blends with that following. 

 Cells in this phase are found in ovaries of embryos about 22 mm. 

 long, and as late as ovaries of mice a day or so after birth. 

 Follicle formation begins at about the time the cells enter this 

 stage. Practically all the early diplotene cells are in primary 

 follicles, made up of a single layer of flattened cells. Later 



