PllONKOMEMA ilAWAllEXSlS. 83 



tion covered the entire animal save the anterior tip and the lips, where the color 

 was light lemon-yellow. 



As in other members of the genus the atrial opening is subterminal and pre- 

 sents the appearance of an elongated slit encircled by rounded lips. Immediatelj- 

 behind it the ventral furrow takes its rise and extends to the posterior end of 

 the body where it becomes continuous with the subterminal cloacal opening. 

 Sections show a well-defined dorsal sense organ with small surrounding spines 

 (Plate 32, fig. 10) but owing to the debris encrusting the body this was not exter- 

 nally visible. 



With the exception of the ventral furrow the body is covered by a relatively 

 thick cuticle that must be an efficient means of protection and at the same time 

 render the animal relatively sluggish. As usual innumerable calcareous spicules 

 are imbedded in the cuticle, forming five or six irregular layers. These spines 

 are of two distinct types; one, the larger and more abundant form with rounded 

 extremities (Plate 37, fig. 5a) is placed more or less parallel with the hypodermis 

 while the second (b) extends at right angles to it and projects slightly above the 

 external body surface. Spines of somewhat this same general form are located 

 along the ventral furrow and alxiut the atrial and cloacal openings; but in their 

 mode of development and owing to numerous intermediate stages it may be 

 seen that they belong to the first class. .\ more detailed description of the 

 position and development of the spines of this species is given on page 28. 



The cuticle is penetrated also by many papillae whose arrangement and 

 general appearance are shown (Plate 33, fig. 3). .\s Hansen has noted they 

 appear like so many baloons situated iimiediately below the external surface 

 of the cuticle and connected with the hypodermis by a slender fibre. This 

 distal expanded part appears to consist of several cells each with basally placed 

 nucleus and an outer vacuolated section which usually fuses with the correspond- 

 ing part of the other cells. These elements pass without any .sharp line of de- 

 marcation into the stalk that contains from four to six elongated nuclei and in 

 turn unites without definite cell boundaries with a small number of cells of the 

 hypodermis. In manj' cases delicate fibres may be traced from these hypodermal 

 cells into the deeper tissues of the body, and at the anterior end of the animal 

 they may occasionally be followed into close proximity to the ganglionic layer 

 surrounding the atrial wall; nevertheless while appearances seem to favor the 

 belief that these are nerve fibres and the papillae are sense organs the evidence 

 is not complete. 



The pedal gland is coextensive with the foot and consists of two long slender 



