174 GEORGE W. CORNER 



However, when an attempt is made to classify all the elements 

 of the fully formed corpus luteum, the picture is complicated 

 by the fact that numerous cells are found which are intermediate 

 in size between the two classes described above, and whose 

 cytoplasmic vacuoles and fatty inclusions are of nature too in- 

 different to place them definitely with either granulosa or theca 

 derivatives. The evidence, therefore, is not yet conclusive as to 

 the exact fate of all the theca lutein cells. Either the inter- 

 mediate forms represent genuine transitional stages in the for- 

 mation of 'lutein cells' from theca interna cells or else they are 

 merely cells, actually of one line or the other, in which the 

 all too slight distinguishing features of the type (size, form, 

 lipoid inclusions and vacuoles) have not been obvious. Toward 

 the latter view 7 — the intermingling of the two cell lines without 

 actual conversion of one into the other — the author is inclined 

 to lean, without more positive evidence than has already been 

 given. 



As a digression, it may be mentioned that some few of the 

 theca lutein cells retain the primitive characteristics of the 

 theca interna, even exaggerating them at times; they are vari- 

 able in shape and size, they have a cytoplasm which stains deeply 

 with acid stains, becoming dark blue, brown, or even orange with 

 Mallory's triple stain and very dark with iron haematoxylin; 

 the cytoplasm is usually somewhat shrunken, and contains clear 

 vacuoles about 1^ to 2/x in diameter, which are quite uniform 

 in size, are closely packed, and which either stain intensely black 

 with osmium tetroxide or remain as vacuoles. The nuclei are 

 often very dense, even pyknotic, and sometimes stain bright 

 orange with Mallory's stain. The cells are often spindle-shaped, 

 branched, or compressed in such a way that they give the ap- 

 pearance of amoeboid motion, as if they were active wandering- 

 cells. These are the cells described in my paper of 1915 as 

 "additional cells of the corpus luteum, type 2" (fig. 2). Al- 

 though their origin is now explained, I have no more light upon 

 their nature or possible function than before. They appear to 

 be more common in the earlier half of pregnancy, but their num- 

 ber varies greatly from animal to animal. 



