634 Prof. Dendy. Structure, etc., of the Pineal Organs [June 22, 



in Angiiis and Lacerta the pigment is lodged in the radial supporting fibres. 

 According to my own observations on Sphenodon, the pigment granules lie 

 between the various constituents of the retina, and are brought in from 

 outside the eye by wandering pigment cells. Such cells are abundant in 

 the connective tissue around the eye, between the inner and outer capsules, 

 and sometimes they also occur in the form of pigment-balls in the cavity 

 of the eye itself, having apparently passed through the retina without 

 breaking up and discharging their contents. Usually, however, they appear 

 to break up in the outer part of the retina, and the granules which they 

 contain stream in in radial lines and streaks between the radial fibres and 

 sense-cells, to such an extent as greatly to obscure the histological structure 

 of the retina. The wandering pigment-cells may possibly obtain their 

 pigment granules from the very large stellately branched pigment cells 

 which lie in the dura mater outside the capsule of the pineal eye. 



The pigment is especially abundant towards the margins of the retinal 

 cup, near its junction with the lens, and here accessory cavities are not 

 infrequently developed in the retina, each surrounded by radiating streaks of 

 pigment granules. The lens contains only occasionally a very few pigment 

 granules. The vitreous body also usually contains very little if any pigment, 

 but occasionally a good deal. 



At stage E, when the pigment first appears, it is found only in very 

 minute granules, chiefly, if not entirely, in the inner part of the retina. In 

 the adult much coarser granules appear, though the small ones can still be 

 recognised in the innermost part of the retina. 



Perhaps the most novel results obtained are tliose which concern the lens 

 of the pineal eye, which is shown to be a glandular organ, secreting part, at 

 any rate, of the vitreous body. At a very early stage in development we 

 can recognise two /ones in the lens, an outer or marginal zone, in which 

 the cells remain undifferentiated and continue to divide actively by mitosis ; 

 and a central portion in which the cells become greatly elongated at right 

 angles to the two surfaces of the lens, which thereby becomes greatly 

 thickened in the middle. Growth of the lens is probably effected mainly 

 by the marginal zone of actively dividing cells, but it is not impossible that 

 the cells may continue to divide after elongation. The distinction between 

 the central and marginal zones of cells persists to a very late stage in 

 development, though posHil)ly not in tlie adult. 



In the adult the arrangement of the elongated cells becomes far less 

 uniform, and they are irregularly curved so as to appear cut through in 

 various directions in vertical Kcctions. They ))rol)al)ly extend right through 

 from surface to surface of the lens, but their inner (snds are somewliat 



