332 HARRY H. CHARLTON. 



EXPLANATION OF PLATES. 



All the drawings are from sections of unfertilized eggs in the Fallopian tube 

 or uterus. They were made with the aid of a camera lucida, and with the exception 

 of Fig. 5 are reproduced at a magnification of 900 diameters. 



ABBREVIATIONS. 



a, zona. b, mitochondrial body, c, phagocytes, d, vacuole. e, degenerating 

 protoplasm. 



PLATE I. 



FIG. i. (48 hours.) Egg with the second maturation .spindle. Polar body 

 shows chromosomes arranged on the spindle fibers. Eggs of this type, showing 

 no changes are found in the tube up to forty-eight hours after parturition. 



FIG. 2. (56 hours.) In this egg the spindle is present but the chromosomes 

 seem to have clumped together more than in Fig. i. The spindle of the polar body 

 has disappeared and in its place are seen two resting nuclei. 



FIG. 3. Polar body (60 hours) from same mouse as Fig. 5 showing many resting 

 nuclei formed from the breaking down of the polar spindle or by the chromatin 

 fragments often observed in the polar body. 



FIG. 4. (48 hours.) Showing the fragmentation of the polar body. Here 

 the first polar body has divided once and one of the parts has redivided. The 

 spindle cut somewhat obliquely is one of few showing good achromatic fibers. 

 These fibers seem to end in a centrosome-like body. 



FIG. 5. (60 hours.) Chromosomes of the second maturation spindle breaking 

 down and forming resting nuclei. Vesicular lobes are seen extending out from the 

 main vesicle. Quite a number of the chromosomes have not yet entered into the 

 process and are seen in the lobes of the forming nuclei. This mouse had a tumor 

 in one of the uteri which prevented fertilization, while on the other side, eggs in 

 the tube had reached the four cell stage. (X 1,800.) 



FIG. 6. (78 hours.) A later stage of vesicle formation from the maturation 

 spindle. Chromatin all in the vesicles, no chromosomes as such. This was one 

 of the few eggs in which the zona was missing. Many dark staining granules sur- 

 rounded the egg and in among them several phagocytes. One phagocyte shown 

 at left of polar body, which is much smaller than normal, suggesting that the 

 phagocytes have been acting upon it and probably upon the zona also. 



