92 PROFESSOR RAY LANKESTER. 
of a pigment introduced through the alimentary canal being 
eliminated by gland-cells in any part of the body in an unal- 
tered condition, or at any rate so little altered (? milk). 
The epidermic cells of the Canary separate the pigment of 
cayenne-pepper when the bird is fed with that substance, in 
such a way as to colour the feathers orange, though no other 
tissues are affected by the colouring matter. I have not been 
able to find any histological or physiological investigation of 
this phenomenon, which, although the mother-cells of the 
feather cuticle cannot be regarded as gland-cells, appears to be 
the nearest parallel known to the case of the green Oyster. 
It is true that indigo-carmine is separated by the liver, 
kidneys, and other tissues when introduced into the animal 
body; but it is necessary to introduce the indigo-carmine 
directly into the blood and not through the mediation of the 
alimentary canal. It is also important to note that the class 
of secreting cells affected by indigo-carmine as well as the 
ready change of this body into a colourless compound, render 
the case presented for the study of the physiologist by the 
secretion-cells of the green Oyster’s gill, altogether distinct and 
of unique interest. 
Possibly the pigment Marennin might be found capable of 
application to the study of some of the phenomena of secretion 
in other animals besides the Oyster, if experimentally intro- 
duced into the alimentary canal in sufficient quantity. It 
would not be difficult to procure the pigment either from the 
Navicula (dried in large masses) or from the green Oyster. 
VII. Free Ama@zorp ConpiItTION oF THE SECRETION-CELLS 
oF THE OystER’s GILL.—A very curious condition is commonly 
exhibited by the secretion-cells of the Oyster’s branchial epi- 
thelium. They are to be found free on the surface of the 
epithelium and exhibit slow amceboid movements. At first I 
supposed that these liberated epithelial cells must be indepen- 
dent amceboid organisms, but a closer examination left no’ 
doubt that they were secretion-cells which had been detached 
from their position, and were leading a free wandering exist- 
