198 FRANCIS H. A. MARSHALL. 
Stratz, Honoré, van der Stricht, Cohn, Sandes, Volker, and 
the present writer, all of whom agree in adopting this theory, 
may be summarised as follows: 
The lutein cells of the fully-developed corpus luteum 
represent the epithelial cells of the undischarged Graafian 
follicle. These cells, after rupture, undergo an enormous 
hypertrophy, which may be accompanied in the earlier stages 
by mitotic division, but usually only to a relatively slight 
extent (Ovis, Vesperugo, etc.). Meanwhile, the thickness 
of the wall of the developing corpus luteum is further increased 
by an ingrowth of connective tissue from the side of the 
follicle, forming eventually an anastomosis of cells, generally 
fusiform in shape, between the hypertrophying follicular 
epithelial cells. This connective tissue is derived either 
from the theca interna alone (Mus, Tarsius, Tupaia, 
Sorex, Dasyurus, Vesperugo, etc.), or it may arise from 
both theca interna and externa (Lepus, Ovis, Spermo- 
philus). The formation of the anastomosis is accompanied 
by an ingrowth of blood-vessels, which gradually increase in 
number throughout the young corpus luteum. The theca 
interna may become entirely spent in this process (Mus, 
Tarsius, Tupaia, Sorex, Ovis, Dasyurus), or certain 
strands of this layer may remain outside the hypertrophied 
epithelial cells after the complete formation of the corpus 
luteum (Lepus, Spermophilus, Vesperugo, etc.). Cer- 
tain cells in this layer are stated in some cases to become trans- 
formed into lutein cells (Vesperugo, etc.). The cavity of 
the discharged follicle becomes completely filled in eventually 
by the further growth inward of connective tissue accom- 
panied by blood-vessels. 
The corpus luteum may attain to very great dimensions, 
this structure, when fully formed, in the cow, having a 
diameter of from two to three centimetres, according to 
Schmidt.! Its large size is all the more remarkable in view 
1 Schmidt’s paper, besides containing observations on the corpora lutea, has 
also an interesting account of the variation noted in the duration of the 
cestrous cycle, or the interval between two successive “heat” periods, in 
