i 44 DISCOVERY REPORTS 



highly probable that the degeneration may be slow, but it is not certain that it always 

 proceeds at the same pace; in no. 436, which was killed in May, there was a well- 

 developed corpus relating to the foetus of 10-2 cm., and in the other ovary there was an 

 older corpus which showed the normal gross structure in a comparatively undegenerate 



state. 



The corpora lutea in the post-ovulation ovaries range from 1-5 to 3-2 cm. in their 

 longest diameter, about two-thirds of them being over 2 cm. Fully luteinized corpora 

 are found in association with uterine epithelium of 30, 17 and 13 ^, and they vary from 

 2-2 to 2-3 cm. in diameter. In three seals, very recently post-partum, the corpora were 

 2-3, i-8 and 0-59 cm. ; all these animals were already in a state of oestrus. As many as 

 three corpora may occur, although in most of the seals examined only one was present ; 

 in six there were two and in three, three, but at no time were signs of a greater number 

 found. The temporary persistence of corpora lutea permits adequate explanation of the 

 presence of more than one. For example, no. 421 was in a post-partum condition as 

 well as early post-ovulation ; therefore, of the two corpora in her ovaries, one was that of 

 the late pregnancy and the other that of the later ovulation, and the condition of nos. 489, 

 491, 492 and 518 was comparable. No. 412 was at the height of oestrus, it had just 

 ovulated and coitus was observed ; there were two corpora lutea in one ovary (which is 

 unusual) and the animal was in a recent post-partum condition. I conclude that of the 

 two corpora, the smaller, of irregular shape, represented a sterile ovulation which had 

 been succeeded by that to which pregnancy supervened, and that the older corpus had 

 survived the whole of pregnancy in a recognizable state. 



The animals in which three corpora can be identified, nos. 424, 504 and 519, all show 

 signs of comparatively recent pregnancy and are in a post-ovulation stage ; they do not 

 really differ from no. 412 which has just been discussed. The oldest corpus is always very 

 degenerate. 



Uterus. (See Pis. XXXI and XXXII.) The resting epithelium is very low columnar 

 or even cubical, about 87 /^ in height. With the progress of oestrus there is an increase 

 in height and 52^ may be attained (no. 414). With the approach of oestrus there is 

 fairly widespread degeneration of the cells, as is shown by vacuolization of the cytoplasm 

 and pycnosis of nuclei ; the vacuolization diminishes markedly in the later part of this 

 phase. Pycnotic nuclei can almost always be found by search in the uterine epithelium, 

 but they are far more plentiful in oestrus and particularly so in the earlier stages, which 

 may be more correctly described as pro-oestrus. These nuclei are frequently, if not 

 always, thrust out into the lumen of the uterus as regeneration takes place. Mitotic re- 

 generation proceeds almost simultaneously with destruction, and at the end of oestrus 

 the epithelium is high columnar with elongated nuclei situated about the middle of the 

 cells. The post-ovulation condition is sharply marked by the disappearance of mitoses 

 and vacuolization and a great reduction in the proportion of pycnotic nuclei. In post- 

 oestrus the epithelium gradually subsides until it reaches the height of the resting stage. 



The stroma passes from a compact condition to one of oedema during oestrus, 

 becoming once more compact in the post-ovulation state. The uterine glands of the 



