ON GREEN OYSTERS. 93 
ence on the surface of the gill, probably on the way to disinte- 
gration accompanied by production of a mucin-like substance. 
In Pl. VII, fig. 14, a number of isolated secretion-cells from 
the gills of the green Oyster are drawn. The upper more 
spherical forms were obtained by teazing; the lower figures 
with long pseudopodia-like processes are secretion-cells which 
have spontaneously assumed the free condition. The assump- 
tion of the amceboid phase by an epithelial cell is not by any 
means an improbable phenomenon although its occurrence in 
normal conditions has not, I think, been previously noted. 
If it is thus possible for a constituent cell of an epiblastic 
epithelium to acquire amceboid characters, and to crawl over 
the surface of the epithelium of which it was once a constituent 
element, the supposition is also admissible that constituent 
cells of an epithelium should on acquiring ameeboid characters 
move in the opposite direction and sink below the epithelial 
basement membrane, in order to enter into relation with the 
mesoblastic tissues. The fact observed in the Oyster’s branchial 
epithelium suggests these possibilities, and has a value—ad- 
mittedly a small one—in relation to recent suggestions as to 
the mechanism of the absorption of solid particles through the 
agency of the epithelium of the alimentary tract in higher 
animals. 
Summary.—The new points which are brought forward in 
the present article bearing upon the “ Green Oyster question,” 
in addition to the general discussion of previous theories, are 
the following : 
1. The description and illustration of “‘ Marennin,” the blue 
pigment of Navicula ostrearia. 
2. The occurrence of Navicula ostrearia in the intestine 
of the green Oyster. 
3. The description and illustration of the secretion-cells of 
the epithelium of the branchie and labial tentacles of the 
Oyster in which the Marennin absorbed in the intestine of 
green Oysters is deposited, and to which accordingly these 
parts owe their green colour. 
