194 
ROBERT SCHARFF. 
the skin of Priapulus caudatus and Halicryptus spinu- 
losus, viz. a cuticula and a subcuticular layer or hypodermis. 
To these two layers I have to add another extremely thin 
one consisting of connective tissue (fig. 8, d.). It does not 
reach half the thickness of the cuticula in the proboscis, while 
in the body or trunk it is still thinner, and could only be 
clearly demonstrated in a few places. 
In Sipunculus nudus this cutis is well developed, and is 
the seat of secreting glands and accumulations of pigment. 
The Cuticula. 
The cuticula covers the whole body, varying in thickness in 
the different parts. At the oral aperture it turns in, coating 
the interior of the oesophagus. On the body, especially at the 
posterior portion of that of Halicryptus, the cuticula reaches a 
considerable thickness. 
It is composed of two parts (figs. 1, 2, 3), an external thin 
homogeneous layer ( ce .) and an internal thicker one (ci.) also 
lighter in colour, which is distinctly stratified. In cutting 
sections for the microscope it often happens that the whole of 
the cuticula or some of the outer layers split off, and thus 
show undoubtedly that it is made up of distinct strata. Reti- 
cular markings are seen on the surface of the cuticula on the 
proboscis. They are generally in shape of polygonal figures 
and correspond to the cells of the hypodermis below, which 
have the same form in a surface view, and from which the 
cuticula has been secreted. 
According to Horst 1 the cuticula of the so closely-allied 
Priapulus bicaudatus appears to possess a honey-combed 
structure, which is produced by two systems of vertical lamellae 
crossing one another, dividing it into a series of prisms. The 
same writer agrees with Ehlers as to the cuticula of Priapulus 
being insoluble, while that of Sipunculus nudus has by 
Andreae 2 been shown to be soluble in boiling caustic potash. 
1 Horst, “ Anatom ie von Priapulus bicaudatus,” ‘ Niederl. Archiv f. 
Zoologie/ Supplement to vol. i, p. 16. 
2 Andreae, “Beitrage zur Anatomie und Histologie des Sipunculus 
nudus,” ‘ Zeitschr. f. wiss. Zoologie,’ vol. xxxvi, p. 207. 
