70 I. W. Rowlands 



I have confirmed the presence of these large follicles in the 

 guinea pig ovary during pregnancy and their staining reaction, 

 as noted by Loeb, forms a ready means of their distinction 

 from any other follicles that are present. They are, quite 

 clearly, follicles that are undergoing the changes associated 

 with the pre-ovulatory phase of development. In no single 

 case has any evidence of spontaneous ovulation been found 

 during pregnancy. The object of the present work has been to 

 discover if ovulation can be induced during pregnancy and to 

 study the growth of the resulting corpora lutea in the presence 

 of those associated with gestation. However, before embarking 

 on this experimental procedure it was necessary to make a 

 quantitative study of the development of the corpora lutea of 

 the cycle and of pregnancy for, to my knowledge, no work of 

 this sort has been published. The experiments form part of an 

 investigation into the capacity of the guinea pig to maintain a 

 second concurrent pregnancy. 



Material and Methods 



All the guinea pigs were of the Hartley-Dunkin (M.R.C.) 

 strain, of which eighty were used to establish the normal 

 growth of the corpus luteum of the cycle and after mating 

 with a sterile or fertile male. A vasectomized male was used 

 to effect sterile mating. All observations were dated from 

 the post-partum oestrus to ensure that every animal was 

 fertile and that each one contributed to the replenishment of 

 the stock before being put to experimental use. The times of 

 parturition and post-partum mating were accurately recorded 

 for those animals used to obtain early developmental stages 

 of the corpus luteum, but for later stages the occurrence of 

 mating was presumed by the discovery of a vaginal plug or by 

 sperm in a vaginal smear. 



Chorionic gonadotrophin, used to induce ovulation, was 

 injected into one of the small ear veins and the result observed 

 by examination of tubal washings for eggs or by the serial 

 section of the Fallopian tubes. The ovaries and the repro- 

 ductive tract were fixed in Bouin's fluid overnight and serial 



