230 STROPHOMENIA AGASSIZI. 



Innumerable spicules are buried beneath its surface and form, roughly, seven or 

 eight layers. The greater number of spines, hollow, needle-like, slightly curved 

 structures rounded at both ends (Plate 1, fig. 3) form two series crossing about 

 at right angles. Among these are many radially directed spicules, Ukewise 

 hollow but with the basal extremity truncated or slightly rounded (Plate 1, 

 fig. 3). 



The hypodermal cells are small and their boundaries indistinct, yet there 

 are many examples of spicule formation where several cells may be seen attached 

 to the base of the spine, and again many cases where but one cell has been 

 detected attached to the radially directed spicules. In examples of the first 

 class the matrix cells lose their connection when they become non-functional. 



The papillae (Plate 1, fig. 2), each attached to the hypodermis by a rela- 

 tively thick stalk, are numerous and are crowded together at the surface of the 

 body. In the expanded portion are a number of nuclei, twenty is the average 

 of six examples, and with these there are frequently darkly staining globular 

 masses that appear to be some glandular product. 



The anterior pedal gland, while extending from the brain to an even greater 

 distance beyond the outlet posteriorly, is in reaUty not a voluminous structure 

 as the cells are not compactly arranged nor do they fill to any great extent the 

 visceral cavity. Owing to the fact that the secretion stains an inky hue in 

 haematoxyUn nothing has been determined regarding the finer structure of this 

 organ, which otherwise presents no especially noteworthy features. 



The outlet of the anterior pedal gland (Plate 1, fig. 4), though not espe- 

 cially voluminous, is of considerable length. Its walls, as usual, are ciliated 

 but otherwise are unmodified save that they are produced into a fold, on 

 each side of the cavity, that becomes gradually lower and finally disappears 

 posteriorly. Halfway back the foot appears as a low ridge in the mid fine, 

 that soon reaches its average size, and posteriorly is continuous with the cloacal 

 chamber. 



The posterior pedal gland differs from the anterior merely in size, and 

 otherwise requires no further description beyond the statement that it disappears 

 an unusually long distance from the posterior end of the foot (in the specimen 

 studied, opposite the posterior end of the pericardium). 



The atrial opening, subterminal in position, leads into a relatively large 

 cavity provided, in typical fashion, with ridges and cirri. Of the former the 

 innermost is considerably larger though the cells composing it are on the average 

 of less height than those of the inner ridge. As may be seen (Plate 1, fig. 4) 



