54 H. M. BERNARD. 



the inner limb is never swollen up with refractive matter. 

 This sparing of the inner limbs in the Amphibia may 

 perhaps be correlated with the enormous size of the outer 

 limbS; for, so far as I know, no other group of animals has 

 them so large in proportion. In the frog they are immense 

 cylindrical vesicles, sometimes as much as 60 ju long and 

 9 to lOjU in diameter. These, then, form very capacious 

 reservoirs for the absorbed refractive matter, and, perhaps, 

 seldom require, during any single period of activity, to 

 overflow into the inner limb. In this way the matter may 

 be dealt with by the outer limb itself, and, apart from the 

 ellipsoid, escape directly into the retina along the wall 

 of the inner limb without entering it. That the refractive 

 matter escapes directly from the outer limbs into the retina 

 along the walls of the inner limbs can sometimes be actually 

 seen (fig. 25, a, h, c). These cases are all from the South 

 African tadpoles referred to in Part III, which, owing to the 

 immense quantity and dark colour of the pigment, are 

 very instructive in this connection. 



(2) Equally decisive for our contention are my sections of a 

 human retina (the healthy normal eye having been excised 

 for a morbid growth on the eyelid).^ This eye had clearly 

 not been much exposed to light before excision. We conse- 

 quently find the outer limbs of the rods free from all 

 refractive matter, and, like the inner limbs, almost clear 

 vesicles but for the longitudinal fibrils and the granules 

 taking nuclear stain. The fibrils on the inner limbs are dotted 

 like those of the outer limbs in the Amphibia (see Part II and 

 figures). Naturally no thick refractive streams can be seen 

 running up into the retina from these rods. In very strong 

 contrast with this are fig. 31, a, h, from retinas of the South 

 African chama baboon,^ which live in the full glare of the 



' Kindly fixed iu Pereiiji's fluid and preserved for me by the well-known 

 oi)litluilinic surgeon, Mr. E. Treacher Collins. 



■■^ They were generously obtained specially for the purposes of these re- 

 searches by Mr. J. C. Rous, Tafel berg Station, Cape Colony, tlirough the kind 

 intervention of our mutual friends, Mr. and Mrs. Mallinson, of the Ilex 

 River Valley. 



