Implantation in Pedetes capemis is superficial and antimesometrial with the embryonic disc mesometrially oriented. As the blastocyst expands, the embryonic pole trophoblast proliferates and penetrates the epithelium a t the mesometrial side to establish a massive trophospongial preplacenta. Maternal blood lac inae form in this, and a preplacental maternal circulation is soon established. Amniogenesis is tiy folding. A choriovitelline placenta develops on the preplacental surface. Yolk sac inversion is k t e . The bilaminar omphalopleure is permanent. Syntrophoblastic tongues penetrate the preplacenta and surround maternal spaces lined with an attenuated trophospongial cell layer, thus providing a hemodichorial barrier when the vascular allantoic mesoderm invades these tongues to form the lobular labyrinth. A typical countercurrent bloodflow occurs. A small allantoic diverticulum persists to term. Several fetal membrane characters, known to be evolutionarily "consurvative," are alike in Pedetes and the more primitive sciuromorphs. These are the type of implantation, amniogenesis, yolk sac inversion, and allantois. The massive trophospongial preplacenta (Trager) suggests affinity with the Myomorpha and Hystricomorpha, but this is a h ghly variable character within the Rodentia. Therefore, it is concluded that on the basis of th: fetal membranes the Pedetidae are somewhat specialized sciuromorphs.

Early gerbil development was studied from days 4 through 12 of gestation. Implantation occurs on day 8 in a shallow antimesometrial implantation crypt. The proamniotic cavity forms from an invagination of basal trophoblast and a folding together of the rim of the cup thus produced. The approximation of this rim gives rise to the ectoplacental cone. The further development and expansion of the ectoplacental cone is much like the rat. Amniogenesis is by folding into the proamniotic cavity. Between large glycogen-filled decidual cells occur many PAS-positive eosinophilic granular cells. A massive subplacental gland forms from proliferating uterine epithelium within the decidua basalis. Epithelial proliferation begins shortly after implantation, and soon short thick cellular processes extend from the antimesometrial side of the lumen whereas long branching cords penetrate the decidua basalis mesometrially. The function of this structure is unknown.

In order to determine if the well known uterine inhibition of the guinea pig corpus luteum is a local effect, a series of partial hysterectomies were performed. Some groups were subjected to one-half or three-fourths hysterectomies alone, while in others one ovary was also removed on either the side retaining some or the side losing all uterine tissue. In addition, two groups in which all ovarian and uterine tissue was preserved were subjected to unilateral or bilateral complete surgical separation of all communicating structures between uterus and ovary. Sham-operated, totally hysterectomized, and unilaterally ovariectomized groups were used as controls.In all groups in which an ovary left in the animal was separated from direct contact with its uterine horn, the estrous cycles became long and erratic, or were arrested completely due to the persistance of active corpora lutea in those ovaries. However, corpora lutea regressed normally in all ovaries left in their normal relationship to a uterine horn. These results indicate that the uterine regulatory factor does reach the ovary by some local route.The mammalian uterus has, since ancient times, been known as the organ in which the young undergo embryonic development, yet only within the last 45 years has it been suspected of playing a more subtle role in the physiology of reproduction. Experiments conducted by Loeb (' 23, '27) upon the guinea pig demonstrated that, in at least this one form, the uterus is capable of contributing to the regular cyclic rhythmicity of the ovary by periodically curtailing the functional life of the corpus luteum. Loeb found that removal of the uterus a few days after estrus resulted in a sudden and complete cessation of all cyclic activity for a period much longer than the normal duration of pregnancy. The corpora lutea in these anestrous animals were evidently in a state of high activity; they were larger than those of pregnancy, and were composed of large polygonal cells, many of which were in mitosis.Histological examination of the vagina and mammary glands gave additional evidence that the corpora lutea were actively secreting progesterone. Since Loeb's work, this phenomenon in the guinea pig has been amply confirmed by many others, and has been proven to exist in other mammals. In all cases where hysterectomy provokes a disruption of the sexual cycle, the corpus luteum is maintained in an apparently functional state. AM. J. ANAT., 121: 425-442.Loeb's experiments quickly stimulated interest in the field of utero-ovarian relationships. Studies were made of many different mammals to determine whether the effect of hysterectomy was of a more general occurrence. In recent years, it has also been found that distension of the uterus results in the opposite phenomenon, the early regression of corpora lutea and concomitant shortening of the estrous cycle (Moore and Nalbandov, '53). The results of the various types of experiments performed during these years fall into three main groups. No apparent uterine influence onthe ovary ...

The present study is an analysis of the effects of superovulatory doses of gonadotropins on the rate and time of ovulation and ovarian histology in immature gerbils. Groups were treated with various combinations of pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (HCG). The maximum superovulatory response followed treatment with 10 IU PMSG and 20 IU HCG. High dosages of PMSG inhibited superovulation, as did some combinations involving the highest dose of HCG. Entrapment of ova within corpora lutes was common in groups receiving high doses of either gonadotropin. Luteal regression, appearing by day 3, occurred often in groups receiving high doses of HCG. A dose of 10 IU PMSG and 5 IU HCG resulted in both a near maximal superovulatory response and the least abnormal ovarian alteration.

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