1 o8 Source o£ Equine Gonadotrophin 



Three mares were sacrificed between the 6oth and '/oth days of pregnancy. 

 In all instances the cups appeared as elevated oval structures varying in 

 maximum diameter from a few millimeters to 3 cm. They are distributed, 

 sometimes in a circular arrangement, over only a portion of the endometrium 

 in apposition with the chorion. From a cursory examination one might con- 

 clude that they were cotyledons provided as a special means of attachment be- 

 tween the maternal and fetal membranes. Actually there is no attachment of 

 these membranes at this point; rather, the membranes are separated, due to 

 the fact that the cups are filled with a yellowish-brown, waxy, or glue-like 

 material. In mare 4, killed at the 105th day, this material was so thick that it 

 could be peeled out with its almond shape intact. In the other cases, however, 

 it adhered like thick glue to the cup or to the chorion. In our opinion, adher- 

 ence of this material to the chorion explains the one case (K5) cited by Catch- 

 pole and Lyons^ in which the chorion gave a positive response while the 

 endometrium was still negative. We find the potency of the endometrial-cup 

 secretion to be 10 to 30 times greater than that of the cups. Schauder has well 

 illustrated the gross appearance of these cups. 



Histologically the cups have a unique appearance in contrast to the remain- 

 ing endometrium, as also does the chorion overlying these cups. As Schauder 

 has pointed out, the chorion at these points is devoid of villi (pi. 1, figs. 1 and 

 2). Mossman,^ speaking generally, states that chorionic villi are frequently 

 lacking in areas where the chorion does not come in contact with the endo- 

 metrium. No doubt, the separation of maternal and fetal membranes by the 

 endometrial-cup secretion explains the lack of both chorionic and endometrial 

 villi at these points. The epithelial cells of the chorion in the cup region are of 

 the tall columnar type and give evidence of greater secretory activity than does 

 the chorion in other regions. 



The lumens of the uterine glands are greatly enlarged, having a cross- 

 diameter several times that of the glands in other portions of the endometrium. 

 The lumens are filled with secretion and the pouring out of this material 

 accounts in part for the endometrial-cup secretion. Between the Goth and 70th 

 days the necks of the glands are in a poor state of repair; the basal glands have 

 a much healthier appearance (pi. 1, fig. 2). At the 105th day the uterine glands 

 are the conspicuous feature of the endometrial cups (pi. 1, fig. 1 and pi. 2, fig. 

 4). The glandular epithelium is extremely low and still the glands appear to 

 be secreting rapidly (pi. 2, fig. 4). 



The tissue between the uterine glands in the cup area does not present a 

 constant picture. In mare 2, sacrificed on the 63d day of pregnancy, many 

 small cells with scanty cytoplasm are packed between the basal uterine glands 

 (pi. 2, fig. 3). In the upper part of the cup there is evidence of autolysis of both 

 glandular and interglandular tissue (pi. 1, fig. 2). In the other two cases (mares 

 1 and 3), sacrificed between the 6oth and 70th days, extremely large polyhedral 

 cells are present between the glands, though some of the smaller cells similar 

 to those seen in mare 2 are also present (pi. 2, figs. 5 and 6). As the cup from 



