216 PRONEOMENIA ACUMINATA. 



The posterior pedal gland is directly continuous with the anterior from 

 which it differs in no essential particular, save in the smaller size of the cells 

 and their lesser number. The ductules lead to the median fold, or rudimentary 

 foot, and in addition are distributed to the epitheUum of the ventral groove 

 generally as far as the spiculose cuticle. With the posterior termination of 

 the foot in the neighborhood of the external reproductive pore, these cells dis- 

 appear, but close behind the gonoduct exit the wall of the cloaca is supplied 

 with a scattering band of cells of the same character opening along the border 

 of the spiculose cuticle. 



The cuticle is of moderate thickness only and the hypodermis is exception- 

 ally thin and its cells difficult to interpret. The spicules, with which the cuticle 

 is crowded, are of the customary proneomenian type, slender, slightly curved 

 needle-shaped structures (Plate 5, fig. 4) arranged in approximately seven layers. 

 Radially directed spines appear to be lacking excepting in the region of the 

 ventral groove. 



The papillae (Plate 5, fig. 6) appear in life to have been filled with a highly 

 fluid substance that after treatment with reagents largely disappears, leaving 

 the few component cells in a much shriveled condition. In the expanded por- 

 tion five to seven nuclei are usually visible; none appear in the stalk. 



As noted previously the hypodermis is a very thin sheet, and the compo- 

 nent cells are very inconspicuous. The spicule-matrix elements on the other 

 hand are relatively distinct, and maintain essentially the same relations as in 

 Proneomenia hawaiiensis for example. The cells retain their attachment to 

 the spine until the latter has travelled halfway to the surface of the body, and 

 in some cases they retain their connection for a longer period. 



The position of the dorso-terminal sense organ was discernible in surface 

 view, owing to the presence of numerous, small overarching spines though the 

 cavity itself was not visible. In sections it presents the appearance of a hemi- 

 spherical depression composed of very slender cells resting upon the somatic 

 musculature. A unique feature appears in the form of a comparatively large 

 number of gland cells filled with a darkly staining secretion, located about the 

 rim of the pit adjoining the spiculose cuticle. In some instances the cells are 

 in the general hypodermal layer; in other cases they are in the underlying 

 tissue, but in any case they open through intercellular spaces about the margin 

 of the depression. 



There are strong reasons for the belief, first expressed by Thiele, that the 

 anterior enlargement of the digestive tract, with its ciliated ridges and finger- 



