NATURE OF EXCRETORY PROCESSES IN MARINE POLYZOA. 131 
of the tissues have remained uncoloured, the leucocytes have 
taken up a large quantity of the pigment. The appearance of 
a zocecium after exposure to indigo-carmine is shown in fig. 17, 
where numerous coloured leucocytes are seen in the meshes 
of the pigmented funicular tissue. The whole of the blue 
pigment is contained in the vacuoles of the leucocytes (fig. 
19); and, as in the analogous cases noticed by Kowalevsky,’ 
the nucleus is unstained. 
The bright blue colour is acquired only in the younger 
zocecia, most of which possess functional polypides. It cannot, 
however, be supposed that the indigo-carmine has been first 
absorbed by the alimentary canal, and then passed on to the 
free mesoderm-cells, as the pigment is taken up quite readily 
by the leucocytes of zocecia which possess no polypides, at the 
growing-points. Nor, for the same reason, can it be supposed 
that the blue colour is derived from pigment introduced into 
the body-cavity directly from the tentacle sheath of the poly- 
pide, in the manner described by Pergens.? I have, indeed, 
no observations which confirm Pergens’ results with regard 
to the mechanism of the extrusion of the polypide, although I 
am not prepared to deny the accuracy of those results. The 
indigo-carmine observed in the leucocytes has probably been 
derived from traces of the pigment which have diffused through 
the walls of the zocecia; the leucocytes absorbing the whole of 
the pigment which enters the zocecium in this way, and so 
protecting the other tissues from the action of the pigment. 
That the leucocytes of older zoccia, with “ brown bodies ” 
developed or developing, are in a condition physiologically 
differing from that of the zocecia which are nearer the growing- 
points is shown by the fact that the cells, in most of these 
cases, are of a distinct, though not very bright, green colour, 
instead of being blue.*? The bright blue colour always appears 
1 ¢ Biolog. Centralblatt,’ Bd. ix, p. 47, &c. 
2 * Zoolog. Anzeiger,’ xii Jahrg., 1889, p. 508. 
3 According to the results of Kitasato and Weil (‘ Zeits. f. wiss. Mikrosk.,’ 
vii, 1890, p. 241), this would apparently point to the existence of the pigment 
in a reduced condition. 
