4.28 Ww. A. HASWELL. 
The pigment is arranged in the form of a network of glistening 
narrow threads which lie immediately below the surface. 
In some full-grown specimens it occurs in relatively small 
amount, and such specimens may appear of a uniform green 
or brownish-green colour. Usually the largest specimens are 
the darkest in colour. 
The general coloration produced by the presence of the 
symbiotic Algz and of pigment of various hues is a mottling 
of green, brown, and yellowish white, but the pattern which 
results is subject to endless variation. Very commonly there 
is a light (yellowish) spot over the region in front of the eyes 
and otocyst, and one on each side just behind, but this 
arrangement is by no means invariable. The whole animal 
is usually very opaque, and it is in most instances impossible 
to make out any part of the internal organisation of an entire 
living adult specimen. The opacity is due partly to the pig- 
ment and the symbiotic Algv, partly to the presence of 
numerous drops of oily matter in the protoplasm of the cells. 
When the animals are looked at under incident light with a 
simple lens or a low power of the microscope the pigment 
presents a glittering metallic appearance, giving the surface a 
lustre like that of frosted silver. Viewed by transmitted 
light it appears dark and opaque. The pigment is scanty or 
absent in immature individuals. 
Integument and Muscular Layers.—lI have found no 
indication either in sections of specimens fixed by various 
reagents, or of macerated and teased specimens, of the 
division of the epidermal layer into cells.1. Nuclei occur at 
irregular intervals; in diameter they average ‘004 mm. 
Externally the epidermis (fig. 3, ep.) in some series of sections 
appears bounded by a definite layer, which becomes more 
strongly affected by staining agents than the rest. This has 
been looked upon as a cuticle, but is regarded by von Graff 
as formed by the bases of the cilia. I do not think that it is 
1 In Convoluta von Graff (14) succeeded by maceration in isolating 
epidermal cells. 
