CHARACTERS OF SPECIFIC VALUE. 



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 buceal 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-FIGURE 2. Cephalodiscus sibogae. A, colony attached to a stone (x 1J). 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. levinseni. 

 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 



