THE OVUM IN THE AMPHIBIA. 242* 



mation of the envelopes of the ova as they pass through to the uterine or 

 dilated portions of the ducts (A). 



Fig. 4. The female Frog after oviposition, with the organs of digestion and the liver 

 removed to show the condition of the ovaries (p) with their fatty append- 

 ages (q), the hyoid and thyroid muscles (n) (o) (p), the lungs (f) and the 

 contracted state of the oviducts (g), and their uterine enlargement (h) with 

 the rectum (/), and the bladder (m) then beginning again to be enlarged. 



Fig. 5. Structure of the ovarian ovum. 



a. The ovum while still attached to the inner surface of the ovary and pro- 

 jecting into the cavity, exhibiting the dark surface within the ovisac, 

 which is traversed by minute vessels (b). 



Fig. 6. Vertical section of the ovum, showing the situation of the germinal vesicle 

 and the canal in the yelk, which corresponds to the centre of the dark 

 surface of the yelk. 



Fig. 7- The presumed mode of disappearance of the vesicle. 



Fig. 8. Spermatozoa of the Frog, a and b escaping from the vesicle of development, 

 c, as seen on the egg after contact. 



Fig. 9. An ovum with spermatozoa half an hour after impregnation. 



Fig. 10. A small portion of surface of the yelk at the commencement of segmentation, 

 highly magnified, (a.) Yelk-cells at the same period, (b.) The smaller 

 cells of the last, more highly magnified. 



Figs. 11 and 12. Examples of partial impregnation at twenty-eight hours after con- 

 tact with the spermatozoa. 



MDCCCLI. 2 t 



