60 LEO LOEB. 



which we made in the course of our continued experiments serves 

 to clear up this point. 



Two days, sixteen hours after copulation, incisions were made 

 into the uterus of a guinea pig. The weight of the animal at the 

 time of the operation was 550 grams. The incisions were longi- 

 tudinal and extended through both horns of the uterus up to 

 near the point of juncture with the tubes. Besides the longi- 

 tudinal incisions a number of transverse incisions into the uterine 

 wall were made. Eighteen days after copulation uterus as well 

 as one of the ovaries was taken out for examination. The ovary 

 was cut into serial sections. Small follicles in the early stages 

 of development, as well as other follicles in early stages of con- 

 nective tissue atresia were found. In addition there were many 

 follicles in the last stages of follicular atresia. There were also 

 present several young corpora lutea, the center of which was 

 partly filled out by connective tissue, while the center of the 

 cavity had not yet been organized by connective tissue. There 

 were furthermore present corpora lutea in an early stage of retro- 

 gression, as well as yellow bodies, completely atretic corpora 

 lutea. These findings correspond to an ovary about three days 

 after ovulation. 



Microscopic examination of those parts of the uterus which 

 had not been incised during the operation showed cylindrical 

 surface and glandular epithelium with numerous mitoses in the 

 glandular ducts. The fundi of the glands are somewhat smaller. 

 In the lumen of the uterus there are some poly nuclear leucocytes, 

 a greater number of which are found in the ducts of the glands. 

 In the connective tissue of the mucosa as well as in the surface 

 epithelium the presence of several small round cells is noted. 

 There are very few mitoses in the connective tissue of the mucosa 

 which is rich in nuclei. These findings correspond to a condition 

 of the uterus about 3-3 }4 days after copulation. 



Near the tubal end of one of the uterine horns, not far from the 

 usual situation of the ovary there was a small nodule. This 

 nodule was cut in serial sections, and its structure is best ex- 

 plained by referring to the illustrations. 



Fig. I shows the position of the embryo. 



(a) It lies in the neighborhood of the fallopian tube. 



