PRIAPULUS AND HALICRYPTUS. 
197 
dermis in Phascolosoma puntarenae and antillarum. A far 
greater development of the cutis is to be found in Sipunculus, 
which, according to Andreae, 1 consists mainly of areolar tissue, 
and in which secreting glands and pigment cells appear to be 
embedded. 
Sensory and Secretory organs of the Skin. 
In the contemplation of the sensory and secretory organs 
we shall have to consider Priapulus caudatus and Hali- 
cryptus spinulosus separately, there being some difference 
between the two with regard to these organs. I shall first 
mention the general disposition of these organs on the body, 
and then give a description of their form, histological struc- 
ture, and probable function, finishing up with a few remarks 
as to their relation to similar organs in other animals. 
On the proboscis of both of them the small dermal projec- 
tions or “ spikes ” are arranged in numerous longitudinal rows 
which are more regular in Priapulus than Halicryptus. On 
the body or trunk on the other hand there are no longitudinal 
but only circular rows of spikes. The spikes are here so dis- 
posed as to occupy a median position on each annular muscle, 
and thus we get a series of parallel rings of them. In Hali- 
cryptus the spikes are similarly disposed to the end of the 
body, two larger spikes standing on each side of the anus (see 
Sanger, 2 pi. x, fig. 6). In Priapulus irregular masses of 
papillae are scattered about at the posterior end of the body 
(the ordinary spikes being here absent) with the exception of 
the immediate surroundings of the nerve-cord on the ventral 
surface (fig. 4, p.). Little spikes also occur on the respiratory 
appendage. 
1 Loc. cit., p. 208. 
2 Saenger, “ On Halicryptus spinulosus and Priapulus caudatus,” 
‘Transactions of the 2nd Congress of Russian Naturalists in Moscow, 1869.’ 
(Written in Russian.) 
