192 WILLIAM WALLACE. 



stance in the spaces between the fibrils of the egg membrane. 

 If HO, then this substance does not stain either with carmine, 

 orange-hgematoxylinj or picro-uigrosin. 



The above observations on the condition of the follicular 

 epithelium and egg membrane in ChimEera point to the 

 following conclusions : — (1) The egg membrane is formed, 

 in part at least, at the expense of the cells of the follicular 

 epithelium. This is indicated, although not by any means 

 proved, by the fact that where the follicular epithelium is 

 thickest and has greatest number of cells per unit area, the 

 egg membrane is also thickest; and where the follicular cells 

 are fewer and more densely arranged, the egg membrane is 

 thinner and denser. (2) Processes of the follicular cells 

 pass through the egg membrane to its inner limit. Granular 

 matter — stained with hsematoxylin — can be traced through 

 the fibrils of the zonoid layer to the yolk. The appearance 

 of the peripheral portion of the vitellus is roughly indicated 

 in the figs. 29 and 30. Radiating masses of granules, darker 

 than those of the general cytoplasm of the egg, extend into 

 and become lost in the latter. 



The most remarkable feature about the ChimaGra follicle 

 is the great thickness of the follicular epithelium and dif- 

 ferentiation of its cells above alluded to. The arrangement 

 of these cells is very characteristic. The smaller uniform 

 cells form an outer layer next the membrana propria, but 

 extend in wedge-shaped masses between the large specialised 

 nutritive cells. Transitions between the two kinds of cells 

 can be found frequently, although there were never seen any 

 indications of karyokinesis in the large cells. No doubt the 

 ranks of the nutritive cells are renewed from time to time 

 from the small generalised cells. 



Summary. — (1) In immature ova of the teleosteau and 

 elasmobrauch species examined, the cytoplasm of the egg is 

 dili'erentiated at its surface into a perivitelline or zonoid 

 layer of peculiar structure, consisting of closely set, radially 

 arranged protoplasmic fibrils. These fibrils are at first 

 connected with those of the general cytoplasmic reticulum, 



