STUDIES IN THE RETINA. 46J 



maintained that fine protoplasmic processes of the pigment 

 cells are permanently advanced as far forward as the mem- 

 brana limitans externa, and are thus always in contact with 

 the rods. Not in any single one of the retinas of some 

 twenty-five vertebrates I have yet examined, and their number 

 must, I think, now amount to fully one hundred, fixed and 

 stained by all the latest methods, and examined with the 

 best available microscopic lenses, have I been able to find a 

 trace of these processes of the epithelial cells permanently 

 interlocking with the rods. On the contrary, when the pig- 

 ment is I'etracted the contour of the pigment cells is per- 

 fectly straight or rounded as the case may be. Had such 

 processes existed, I am convinced that at least some evidence 

 of their presence would have forced itself on my attention 

 long ago. 



I have, therefore, so far no point of connection to offer 

 between the physiological details here described and the 

 visual purple, which appears when, according to my own 

 observations, the rods should be getting rid of the matter 

 absorbed when last the light forced the pigment cells into 

 close contact with them, and is bleached when they ought 

 to be absorbing, and at the same time clarifying, the warm 

 colouring matter of the pigment. A reconciliation of these 

 observations will doubtless some day be forthcoming, and 

 there the matter must be left for the present. 



The Ellipsoid. — This somewhat inappropriate name is 

 usually applied to the body found in the inner limbs of the 

 Amphibia where these limbs abut against the outer limbs. 

 Max Schultze regarded it as a plano-convex lens; the name 

 here adopted was suggested by Krause ("Opticus Ellip- 

 soid"). It is here pieferred robbed of its prefix ''opticus," 

 so as not necessarily to suggest special functions.^ So far as 

 the terms describe form alone, " plano-convex " is prefer- 

 able to ellipsoid for the Amphibia, for that is the most usual 

 definitive form assumed in the adult rod, i. e. when the 

 rod is not very large and thick, as it is in the axolotl, in 



* Krause tliought it was the nerve-end organ [' Anat. Uutersuch.,' 1860) 



