432 FREDERICK KEEBLE. 
is due partly to orange-red glands occurring in the superficial 
tissues, but chiefly to numerous yellow-brown cells, which are 
distributed fairly regularly in the sub-epidermal and deeper 
tissues of the body. 
Though excellent descriptions have been published by von 
Graff (1891) of the habits and structure of C. paradoxa, 
nothing appears to be known with respect to its yellow-brown 
cells. The origin, development, significance, and fate of 
these cells are alike obscure. 
It is chiefly with these yellow-brown cells that the present 
paper deals. 
The investigations on which the paper is based were begun 
by the writer in collaboration with Dr. Gamble. 
Of the conclusions enumerated in the summary, those to 
which the letters ““G and K ” are appended are the result of 
our joint work. For the others the writer of the paper is 
alone responsible. The research has been conducted in the 
laboratory, Trégastel, Cotes du Nord, and at University 
College, Reading. 
Section IJ.—TuHer Bionomics or C. PARADOXA. 
(a) The Paradoxa Zone.—Convoluta paradoxa has 
its habitat among the finer brown and red seaweeds which 
occur at some little distance below the low-water mark of all 
but the larger spring-tides (Pl. 26, fig. 1). 
The animal is flattened dorsi-ventrally ; its anterior end is 
somewhat blunt, whilst posteriorly the body is prolonged into 
a slender tapering tail (Pl. 26, fig. 5; Pl. 28, fig. 10). The 
lateral margins of the body are flexed ventrally, and form, 
with the ventral surface, a groove whereby the animal is fitted 
saddle-wise over the weed on which it glides. It progresses 
by a gliding motion, and whenever it meets with some minor 
obstacle the sides of the saddle-like flexure give way and 
adjust themselves once again to fit the surface over which it 
is passing. If the animal encounters a more serious obstacle 
it fixes itself by its tail-end, partly by a mucilaginous secre- 
