THE OVARY OF THE SPERMOPHILE 131 
follicles burst and become transformed into corpora lutea, these 
new bodies are the only corpora lutea in the ovary. They are 
all produced simultaneously and they also develop simul- 
taneously if they are not abnormal in some way. 
The picture of the ovary changes, then, when fertilization 
brings on pregnancy. From this time on until the period of the 
growing follicles is reached in the late summer, the ovaries con- 
tain corpora lutea. These are the predominating structures in 
the ovaries of the sprmg and summer. The changes which take 
place in these organs during the period have to do with the 
corpora lutea principally. The following descriptions of ovaries 
will be attempts at picturing them with corpora lutea of various 
ages. As this study is very largely concerned with these luteal 
structures, they will be described in considerable detail. Prob- 
ably the ovaries which contained the very youngest corpora 
lutea seen were those in which ovulation took place in the 
laboratory, the animals being sacrificed very shortly afterward. 
Experiment 268-13 (spermophile 303). Captured May 3, 1916: 
Sacrificed the same day. Weight, 112 grams. 
Gross observations. There are no visible signs of pregnancy in the 
uterus except congestion. The ovaries contain several slightly raised, 
small spherical bodies which resemble mature follicles except that they 
are red or pink instead of colorless. 
Microscopie observations of the left ovary. Fixative, acetic osmic 
bichromate. Stain, acid fuchsin and methyl green. This ovary con- 
tains five luteal bodies, three of which are normal and two of which 
are not. Beside these, there are several growing medium-sized fol- 
licles, no large ones, quite a number of small atretic follicles and a few 
primordial ova. The interstitial cells are not as conspicuous in this 
ovary as they were in some of the ovaries of early pregnancy. All the 
blood-vessels and sinuses in the medullary portion of the ovary are 
very much dilated. Most of the ovary is made up of the five corpora 
lutea. Serial sections of the three normal ones show them to be of 
different sizes from 0.7 mm. x 0.8 mm. in diameter to 1.3 mm. x 
0.1 mm., depending on the amount of blood which they contain, for 
practically all the young corpora lutea contain blood in their centers 
(figs. 13 and 17). A hemorrhage from a blood-vessel in the wall of the 
follicle must occur as the follicle bursts. The exact point of this burst- 
ing cannot be made sure of in any of these structures. Each luteal 
body is surrounded by a very thin connective-tissue capsule, no doubt 
the same theca externa which surrounded the follicle. From this thin 
capsule to the central core of blood are massed the luteal cells. They 
