198 
EOBEET SCHAEFF. 
Priapulus caudatus. 
On the proboscis the spikes are in form of small truncated 
cones, just visible by the naked eye. It has been mentioned 
before that the hypodermic cells which constitute the interior 
of these cones undergo a transformation, becoming very much 
elongated (fig. 1, h.), and converge somewhat towards the 
centre of the base. The cuticula forms the outer layer of the 
cone, and leaves a circular opening at the top. Through this 
opening a number of small delicate hairs are seen to project, 
piercing a thin membrane ( m .) which covers the distal ends of 
the cells. The outer darker layer (fig. 1, ce.) of the cuticula 
does not quite reach the apex of the cone, but only extends 
about half way up and surrounds it as a sort of a sheath. 
Various circumstances have led me to believe that the upper 
part can be retracted into this sheath, although I never 
examined the animal in the living state. Sometimes I met 
with sections in which the upper part was actually partly 
retracted into the lower sheathed portion. Horst’s “ Rippen- 
muskeln,” which run longitudinally underneath the rows of 
cones in the proboscis, probably serve to draw in this upper 
part. Underneath every spike on the proboscis there is a 
hollow space (fig. 1, sp.) in communication with the body 
cavity, which has also been described of Priapulus bicau- 
datus (Horst). 1 I presume that the space which is to be 
found beneath every cone can be rapidly filled with blood, 
communicating freely with the general body cavity, and in this 
way the retracted cone may be pushed out. This view is further 
favoured by the great advantage such a mechanism would 
have as a protection for these slender structures. 
Willemoes-Suhm, 2 who observed living specimens of Pria- 
pulus, tells us that they are in the habit of burying themselves 
into the sand by rapidly pushing out the proboscis, and with 
1 Horst, loc. cit., p. 20. 
s Willemoes-Suhm, “Biologische Beobachtungen iiber niedere.Meeresthiere,” 
‘ Zeitschr. f. wiss. Zoologie,’ vol. xxi, p. 386. 
