€00 William Patten 



On the inner side, the piane of division is at right angles to the tangent, 

 and consequently the hypodermis at that point increases in extent, hnt 

 remains single layered. This caiises an elongation, and flatteuing- of the 

 papilla, the proliferating- point, hy. assuming a position more and more 

 on the outer side. At first the hypodermic core is not at ali sharply de- 

 fined; severa! of the more deeply situated cells (figs. 11, 12 and 16) 

 separate from the rest and mingle with the niimerous connective tissue 

 cells, from which they finally hecome indistiuguishahle. They are the 

 ganglionic cells, which later provide the eye with nerve 

 fibres. The division of the cells, on the outer side of the papilla, soon 

 ceases, and the solid core of deeply staiued nuclei becomes surrounded 

 by a well defìned, single layer of hypodermis, containing dark, homo- 

 geneously stained nuclei (figs. 12 and 16). Several connective tissue cells 

 bave grown, by rapid divison, between the hypodermis and the core, 

 around which they form a single layered capsule of cells loosely con- 

 nected by means of protoplasmic outgrowths. The nuclei are distin- 

 guished from those of the hypodermis by containing a clear, faintly 

 stainable fluid, in which are several minute and iutensely stained 

 bodies, often collected into a flattened piate in the centre of the nucleus. 

 Up to a late period in the development, these characteristics serve to 

 distinguish the connective tissue cells from those of the hypodermis. At 

 the base of the core are several large ganglionic cells, one of which is 

 represented in fig. 12. After the core has been entirely separated from 

 the hypodermis and^enclosed within the connective tissue capsule, the 

 whole papilla becomes elongated and somewhat flattened, while a disc- 

 shaped cavity appears in the centre of the core, transforming it into 

 the optic vesicle, the equally thick anterior and posterior walls of 

 which, at first, consist of a single layer of cells. An inequality in the 

 two walls soon appears, in that the nuclei of the outer, retain their radiai 

 arrangement, while those of the inner become taugentially disposed, at 

 the same time formiug a double layer of lighter colored nuclei (fig. 4). 

 The outer layer of the optic vesicle develops into the retina, while the 

 two inner ones give rise to the argentea, ag. and tapetum, ta. 



The cavity of the vesicle. which becomes more and more flattened, 

 in the earlier stages appears to be filled with a clear fluid, through which 

 delicate, protoplasmic filaments pass from the inner to the outer wall. 



In the following stages, the posterior wall becomes more sharply 

 defìned , and bere , for the first time , the cells of the optic vesicle are 

 provided with distinct celi walls (fig, 5) . The outer row of cells , ag^ 

 andf/^2_ becomes filled with refractive, yellowish green granules, some 



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