ON PHYMOSOMA VARIANS. 7 I 



granular ; and it absorbs staining fluids with a certain readi- 

 ness, while the main body remains in all the preparations 

 quite unstained. The cuticular substance appears in the 

 greater part of the body to be arranged in wavy columns, 

 running more or less regularly at right angles to the surface 

 of the body, and resting each on a single ectoderm cell (fig. 

 10). Each column exhibits a further tendency to a laminated 

 structure, the layers composing it lying concentrically to the 

 body of the animal. 



A result of the peculiar shape of the ectoderm cells in the 

 trunk-region is the formation beneath them of a series of small 

 cavities, containing a coagulum. By a kind of lifting up of 

 several cells from the adjacent muscles, these cavities commu- 

 nicate with one another and so attain a considerable size (fig. 

 10). They communicate with the cavities, to be presently 

 described, which lie between the two layers of the papilla; 



(%-16). 



The function of these channels is in all probability con- 

 nected with the circulation of the nutrient fluids ; but I have 

 not succeeded in tracing a connection between these and any 

 other of the cavities of the body. The analogy between these 

 spaces and the dermal spaces of Sipunculus need hardly be 

 pointed out. A surface view of the skin shows that the 

 cuticle is broken up into a series of fusiform areas (fig. 11). 

 These areas roughly correspond with the skin-papillae, the 

 lines limiting them being formed by thickened portions of 

 cuticle. When the animal is in an expanded condition the 

 areas become thicker and shorter. 



The papillae of the introvert and trunk are entirely ecto- 

 dermal. Their external appearance has already been de- 

 scribed; the arrangement seen in section is shown in figs. 14 

 and 16. 



The cuticle seems, in the region round the base of each 

 papilla, to contain irregular spaces, as if its inner and outer 

 surfaces had been pulled apart, an appearance which may, of 

 course, be due to the action of the knife used in cutting sec- 

 tions. On the papilla itself, the plates seen in surface views 



