58 Nils Hj.-Odhner. — 
condary condition, a result of the parasitic mode of life attributed 
to most of the Solenogastres. It seems, however, inconvenient to 
design such forms as Nematomenia as parasites only for the 
reason that they feed on Hydroids, a habit which they share with 
other animals by no means parasitic, for example Nudibranchs 
(e. g. Doto). Against the supposition that a parasitic habit may 
have caused the reduction of the radula in Nematomenia there 
may further be objected that other forms which exclusively live 
on Alcyonarians are furnished with a radula (e. g. Anamenia). 
Å parallel to the progressive development of the radula shown 
up above is exhibited in the gradual specialization of the epidermis 
and the cuticula into the complicated structure existing, for example, 
in Proneomenia. The organization of the cuticula and the 
epidermis has also, and with good reason, been taken as a basis 
of classification (cf. SIMROTH 1893, Pruvort 1902, NIERSTRASZ 1908, 
THIELE 1913). In the family Lepidomeniidae THIELE unites genera 
with a thin cuticula containing no hypodermis papillae. Starting 
from this characteristic as the primitive one, we find the simplest 
structure in Gymnomenia where the epidermis is covered with 
simple flattened cuticular plates each coinciding with the outer 
surface of the cells and margined with erect lists. In Lepidomenia 
scale-shaped spicula have developed between these plates and be- 
come imbricated, as is also the case in Chaetoderma and Wirenia. 
This imbrication seems to be due to an increased apposition of sub- 
stance at their anterior end, which thus becomes thicker and broader 
than the posterior, and is sunken; the latter projects backward and 
is raised from the body. Assuming that the epidermis of Chaefo- 
derma has been folded, and that the »Riesencellen« (WIREN) 
have occupied the apices of the folds, we get a type like that 
of Neomenia, where cylindric or bulbiform hypodermis papillae 
project between the spicules. The latter in Neomenia acquire a 
furrow-shaped habitus, which may be derived from the flattened 
spicules of for example Wirenia. From the features just described 
are derived the stalked hypodermis papillae and the hollow needle- 
shaped spicules of Proneomeniidae, which thus appear as the final 
stage in the evolutionary process. 
A total absence of spicula, as in Gymnomenia, must be con- 
sidered as the most primitive condition. We must assume that among 
the primitive epidermis cells spicula-forming ones have subsequently 
developed; thus the epidermis of the Solenogastres forms a parallel 
