FEMALE REPRODUCTIVE CELLS 



471 



sists from the beginning to some time after synizesis. Some of the 

 oogonia are now seen to have not grown or otherwise changed. These 

 are destined to become the nurse or follicle cells. 



We shall not discuss in this form the debatable questions connected 

 with the details of chromatin changes which take place before, during, 

 and after synizesis. The figure shows that in the preceding stages the 

 thread-like arrangement of the chromatin becomes double, and its loops 

 appear to be connected individually with the centrosome-like body. 

 Later, as is shown by other cells in the figure, the thread breaks up into 

 shorter, rod-like bits which are still double. The height of the contrac- 

 tion stage is well shown by two of the other cells in Figure 441. All 

 these closely successive stages form a layer, just inside of the young 



FIG. 442. Pre-oocytes of cat. X 1000. (Compare with Fig. i, which is the fully grown, 

 first oocyte ready for the reduction divisions.) 



oogonia, and farther still inside we may see other stages which show 

 what happens when synizesis is past. 



These later stages show several histological differences. The tubules 

 are being divided into smaller groups by the growth of connective-tissue 

 septa, and it can here be seen that some of the original tubule cells which 

 did not undergo synizesis have begun to divide and surround the young 

 ovum, which must now be called a pre-oocyte. This name is necessary 

 to distinguish it both from the oogonium before synizesis, and especially 

 from the later primary oocyte which goes through the first maturation 

 division. 



The pre-oocytes have all been formed at about the time of birth in 

 the cat, and constitute a layer just under the surface of the ovary. This 

 layer remains here during the greater part of the cat's life, the majority 

 of its cells never changing, while from time to time some of them move 

 a little farther down into the stroma of the ovary and begin a rapid growth 

 period which ends in maturation and discharge. Figure 442 shows 

 several cells from this layer in an adult cat. Among the pre-oocytes 



