THE CORPUS LUTEUM OF PREGNANCY IN SWINE. 75 



chromatin (more than the true lutein cells), and smoothly staining, very finely granular 

 cytoplasm. The cells are round, or slightly elongated in one direction, and are smaller 

 than the lutein cells, having a diameter of 15 to 20 microns. Now, if we examine the figures 

 of some upholders of the compromise or joint-origin theory of the corpus luteum, for 

 instance, those of R. Meyer (1911), we find that they show cells of this same appearance in 

 this same situation, which are described in the text as cells of the theca interna, not yet 

 changed into lutein cells or connective-tissue cells. Are these cells which I have described 

 in the pig identical with the so-called theca lutein cells? The evidence for this view lies 

 in the facts that they are present in the early stages of pregnancy, are then very distinct 

 from the ordinary lutein cells, and lie mostly in the position in which the theca lutein cells 

 are described. Against it is the fact that when the corpus luteum undergoes certain changes 

 to be described later as distinctive of the latter part of pregnancy, these cells seem to increase 

 in number, they follow the growing connective-tissue reticulum into all parts of the corpus 

 luteum, and they come to resemble the true lutein cells very closefy; indeed, at times it is 

 almost impossible to distinguish them; whence it might be inferred that the two sorts of 

 cells are different only in state of activity. The origin of these cells must be left without 

 further definite statement, although we shall come back to them later, as they form part 

 of our criteria for determining the age of the corpus luteum by microscopical examination. 

 Type 2 (fig. 3, b). — These are cells of varying form and size, generally rather smaller 

 than the lutein cells, ranging in shape from spindles to branching and spherical forms, 

 having a cytoplasm which stains deeply with eosin, and takes a dark brown or purple color 

 with Mallory's stain, but sometimes takes instead the aniline blue ingredient of the mixture. 

 Very often the CNdoplasm is filled with minute vacuoles which appear as bright, highly 

 refractile granules about 1 to 2 microns in diameter. No matter what fixing reagent and 

 stain is used, they remain vacuoles, and may even be found in osmic-acid material. The 

 same vacuoles may occasionally be found in the lutein cells. I have not seen these cells in 

 fresh teased preparations. They are not numerous; in one section from a very few to a 

 hundred may be seen scattered among the hundreds of lutein cells, but they are not found 

 in all ovaries, although they are easily seen, because of their dark stain and the fact that 

 their cytoplasm is usually slightly shrunken, and hence they stand out distinctly. They 

 seem to have been observed previously only by Delestre, who saw them, if I interpret his 

 description aright, in the corpora lutea of cows (1910). As to the nature of these cells, it 

 is difficult to say whether they represent a modification of the lutein cells or of the connec- 

 tive tissue. There seem to be transitions in both directions. But there is perhaps a clue 

 in the specimen illustrated in figure 1, of a very recently ruptured follicle, in which the 

 layer of theca interna cells nearest the granulosa is partly composed of cells similar in size, 

 shape, appearance, and staining reactions to the cells in question. The significance of 

 the cells is totally obscure to me. 



CYTOLOGY OF THE LUTEIN CELL. 



The lutein cell possesses the elementary structures found in all animal cells. The 

 nucleus, which in the active stages of the corpus luteum is round, vesicular, and poor in 

 chromatin, has one or more large nucleoli. The cytoplasm, at certain stages to be specified 

 below, is differentiated into two portions: an inner dense zone, the endoplasm, which in 

 fixed specimens appears to be very finely granular, and an outer zone, the exoplasm. This 

 latter zone, whether studied in fresh preparations or in carefully fixed sections, is of the 

 most astonishing complexity. It is so full of granules and globules of diverse substances 



