THE DEVELOPMENT OF THE CORPUS LUTEUM. 195 
undergone by this layer during the formation of the corpus 
luteum than in certain of the other mammals. Biihler had 
suggested that Sobotta might have confused the cells of the 
theca interna during an early stage of ingrowth with those 
belonging to the follicular epithelium, which they undoubt- 
edly at one period resemble, saying that the latter author 
had not properly described the connective tissue sprouting 
into the cavity of the newly-discharged follicle. Sandes’s 
description is of value as showing that Bihler’s criticism loses 
all force when applied to Dasyurus, with which the mem- 
brana granulosa undergoes so considerable a hypertrophy 
prior to the thecal ingrowth as to sometimes almost fill the 
cavity of the follicle, and thus all possibility of a confusion 
between epithelial and connective-tissue cells is precluded. 
Sandes describes also the fate of those follicles which do 
not rupture in Dasyurus. Inthe case of the smaller follicles 
both follicular epithelium and ovum frequently degenerate, 
but the former may persist as a single layer of cuboidal epi- 
thelium. Sometimes a metaplasia of epithelial cells into 
spindle- or star-shaped cells is said to take place, as in other 
animals. In this way the cavity of the follicle becomes filled 
up, or it may be obliterated by the ingrowth of connective 
tissue. Other atretic follicles may for a time remain cystic, 
with a layer of cuboidal epithelial cells, which eventually dis- 
appear. Follicles which have become ripe, or almost ripe, 
however, are stated to pass through changes precisely similar 
to those undergone by corpora lutea, except that the ovum, 
instead of being extruded, degenerates in situ, becoming 
invaded by leucocytes and by connective tissue. 
The corpus luteum in the marmot (Spermophilus 
citillus) has been shown by Volker to be formed in essentially 
the same way as that of the mouse, the rabbit, and the sheep. 
It resembles that of the sheep and (according to Honoré’s 
description) that of the rabbit, in the fact that the thecal in- 
growth is not merely confined to strands of tissue arising 
from the inner layer. It also resembles the rabbit’s corpus 
luteum (according to Honoré) iu that the theca interna need 
