PRIAPULUS AND HALTCRYPTUS. 
195 
Ehlers designates the cuticula of Priapulus as “ chitin 
some investigators, on the other hand, like Graber, 1 seem to 
suppose that its identity with the chitin of the Arthropoda is 
as yet very doubtful. 
The Hypodermis. 
The hypodermis in its various modifications forms the sub- 
stratum to the cuticula. It consists generally of a thin layer 
of about the same thickness as the cuticula. Looking at the 
hypodermis from above it appears as a layer of polygonal cells 
corresponding to the markings found on the cuticula. A cross 
section reveals the shape of the cells, which contain only a 
small quantity of protoplasm, and a comparatively large nucleus 
(figs. 1, 2, 3, h .) . They send out numerous processes on the 
inner surface, by means of which the cells seem to communi- 
cate with one another. 
On the proboscis we find longitudinal rows of little spikes or 
cones projecting from the skin, which will be described later 
on under the head of sensory organs. Their interior is stocked 
with hypodermic cells, which have been drawn out in shape of 
very long threads. In the small papillae on the body of Pria- 
pulus a similar elongation of the cells takes place, while in 
those of Halicryptus they are still further modified into three 
different groups, showing an important diversity of form (figs. 
3 a, 3 b). 
Round about the anus the hypodermis of Priapulus cau- 
datus undergoes a curious modification (fig. 4) in distinction 
to Priapulus bicaudatus and Halicryptus, where this does 
not occur. The cells become very much elongated, but at the 
same time they expand also in width so as to form a compact 
mass (fig. 10), and their protoplasmic contents increase, filling 
up the whole of the cells. 
Ehlers describes these cells “ as a heap of glandular bodies 
lying under the subcuticula,” and Graber 2 says “ Bei geeigneter 
1 Graber, “Ueber die Haut einiger Sternwurmer,” ‘ Bericlite d. Kais. Ak. 
d. Wiss., 5 vol. lxvii, p. 61. 
3 Graber, loc. cit., p. 64. 
