230 BLIND VERTEBRATES AND THEIR EYES. 



the superior ovum, but one possibility is that of a more fortunate situation in regard 

 to the source of nutrition. In most cases, if not in all, the ova which gain in size 

 over the others lie in such a position in the "nest" as to be more nearly in contact with 

 the stromal blood capillaries than the others, and this very likely furnishes the expla- 

 nation of the phenomenon noted. 



In case, for any reason, no ovum in a "nest" develops, all the ova in that "nest" 

 undergo a slow, pigmented degeneration, or atrophy. The evidence for this lies in 

 the presence within the stroma of masses of yellowish-brown cells which do not stain 

 with haematoxylon. For convenience I shall speak of them as the "yellow cells." 

 Their nuclei may be evident only as small, deeply staining masses of chromatin; 

 or the chromatin may have the form of a more or less definite spireme ; but in many 

 cases the nuclear material shows signs of karyorrhexis, being decidedly broken up 

 and apparently migrating into the cytoplasm of the cell. A reference to plate 28, 

 d and E, will show that these cells can not be red blood corpuscles, for, not only do 

 they not lie within a blood-vessel, but they are also more than twice as large as 

 undoubted red blood corpuscles in the same section. They have none of the 

 characters of leucocytes or phagocytes, but they do exhibit the typical brown or 

 yellowish pigmentation of degenerating epithelial cells. 



As shown (st.c, plate 28, fig. d), the yellow cells lie within a space surrounded 

 by exactly the same sort and arrangement of stromal cells as those which inclose 

 undoubted "nests" of ova. Hence they must be regarded as either degenerating 

 ova or cells which have taken the place of ova. As already stated, they have none 

 of the characters of phagocytes. One other possibility is suggested by the fact of 

 the viviparity of these fishes ; that is, the possibility that these yellow cells may rep- 

 resent a sort of corpus luteum. Aside from the structure of these cells, which do not 

 have more than a very faint resemblance to the lutein cells of mammalian corpora 

 lutea, one consideration very effectually disposes of this possibility ; namely, the fact 

 that these yellow cells do not occur in the larger ovaries, i.e., in those of the more 

 mature females, but on the contrary they occur in the smaller and even the smallest 

 ovaries at hand. They certainly can not therefore be of the nature of corpora lutea 

 cells. That they are degenerating ova seems to me the most probable conclusion, 

 for the following reasons: 



(a) The "yellow cells" occur only in masses, exactly similar, in point of 

 number and size of cells as well as in position in the stroma, to the 

 "nests" of young ova. 



(b) The masses of "yellow cells" are surrounded by the same sort and 



arrangement of stromal cells as surround the "nests" of ova. 



(c) The "yellow cells" exhibit the typical brown pigmentation of slowly 



atrophying epithelial cells. 



(d) There are no cells of sufficient size in these ovaries which could have 

 these characters except degenerating ova in "nests." 



These fishes are undoubtedly descended from oviparous forms, and viviparity 

 is probably a comparatively recent acquirement, though most probably attained 

 before the change of habitat from the sea to the underground streams of Cuba. 

 Some at least of the marine members of the Brotulidas are also viviparous. 

 The production of the many "nests," each with its hundreds or even thousands 

 of young ova, is a reminiscence of the oviparous condition, when it was necessary for 



