ON GREEN OYSTERS. 85 
It is important to note that the blue pigment does not occur 
as a cell-sap; does not, in fact, occupy a vacuole or vacuoles, 
but is diffused through the protoplasm only. In some cases 
it seems to impregnate uniformly the whole of the protoplasm 
(figs. 3 and 5), but more usually it is absent from the nucleus 
and the protoplasm immediately surrounding that body (fig. 1, 
6), and is confined to the protoplasm occupying the tips of the 
spindle-shaped organism (fig. 1, d@). 
Usually one, two, or more spherical droplets, of a more refrin- 
gent nature, are to be seen scattered in the protoplasm (figs. 1, 
4, 5, 6, e), and these appear to be more deeply impregnated 
with the blue pigment than is the protoplasm. At the same 
time it is possible that this apparent coloration of the refrin- 
gent globules is an optical illusion, due to reflection of the 
surrounding colour. 
It must be understood, in looking at the drawings (figs. 1 to 
9), that each represents a particular aspect of a Navicula and 
a single optical plane. Thus in some the nucleus is not seen, 
not being in focus; in others the protoplasm is continuous, and 
the vacuoles are not shown owing to a superficial focussing, 
and so on. 
All attempts to dissolve the blue colouring matter failed. 
Neither in bulk nor on the field of the microscope was it 
possible to separate the blue pigment in solution from the 
protoplasm of the Diatom. Weak ammonia caused the pro- 
toplasm to break up into spheres as shown in fig. 9, without 
parting with its blue colour. Distilled water or prolonged 
action of acetic acid caused a further breaking up of the blue- 
coloured masses into minute granules, and their total dis- 
appearance with, so far as I was able to form an opinion, the 
total destruction (and not the solution) of the blue colour. 
The following solvents were ineffectually applied to the 
living Diatoms, no true solution of the blue pigment being 
obtained, viz. distilled water, alcohol, ether, weak alkalis, weak 
acids. 
It is possible that a thorough attempt to obtain the blue 
pigment in solution from a large bulk of dried material, such 
