CHARACTERS OF SPECIFIC VALUE. 5 
visceral mass is 1'5 mm., and from the ends of the plumes to the end of the visceral 
mass about 2 mm. 
The polypides of C. hodgsoni are a little larger than those of C. dodecalophus, and 
those of C. nigrescens considerably so, the length from the front of the buccal shield to 
the end of the visceral mass of the last species being 4°5 mm., i.e., three times the 
corresponding measurement of C. dodecalophus ; but the same ratio is not maintained in 
the width of the body. The polypides of C. levinseni are about as long as those of 
C. dodecalophus, although more cylindrical, and those of C. gracilis and C. sibogae 
(neuter individuals) are smaller. 
The length of the stolon and its mode of curvature, whether towards the mouth or 
away from it, are characters that can only be employed in a very general way for dis- 
Text-FicuRE 2.—Cephalodiscus sibogae.—A, — colony attached to a stone (x 14). B,—a couple of branches 
more highly magnified. The cavity of the tubarium is continuous, and opens by several ostia. (Copied from 
Harmer, 10, plate 1, fig. 2 and plate 2, fig. 18.) 
criminating purposes. The differences depend almost entirely upon the amount and the 
mode of distribution of the longitudinal muscle fibre of the stolon. If, as is usually 
the case, there is more muscle on the antero-ventral wall of the stolon than elsewhere, 
the animal dies with the stolon curled towards the mouth owing to the contraction of 
these fibres in its death struggles, but this curvature is not apparent if the animal dies 
tightly fitted into a tubular space, as do the polypides of C. nigrescens and C. levinsent. 
Some species are remarkable for the great development of epidermal pigment, 
which causes them to appear black. This is so with C. nigrescens and C. sibogae. 
C. gracilis is described as having a median line of pigment, on the anterior side of the 
