Norwegian Solenogastres. 59 
to the mantle in the Mollusca in which a chitineous cuticula as 
well as a calcareous shell is simultaneously secreted by the epi- 
dermis, though at differentiated regions. 
We now pass over to a critical examination of the problem 
concerning the evolution of other organs of the Solenogastres and to 
an inquiry into the affinities of this much discussed group of ani- 
mals. We shall base our argumentation on WIREN’s statements, 
which are grounded on a solid foundation of careful observations. 
If in the following WIrtn's interpretations of the facts cannot 
always be accepted, this is merely due to the fact that the more com- 
prehensive material studied since the publication of WIREN’s works 
has opened up new perspectives. 
Proceeding from the above-mentioned view »dass sich die Radula 
bei den Solenogastren nicht in ihrer ersten Entwickelung sondern 
im Riickschritt oder in der Umbildung befindet« (1892, p. 85), 
WIREN believes that he has found »einen festen Ausgangspunkt 
fir die Erörterung der Frage im Ganzen tuber die Stammesver- 
wandtschaft der Solenogastren. Diese Erérterung wird zeigen, 
dass diese Tiere, wenn sie auch viele Eigenschaften uralten Datums 
beibehalten, doch friher anderen Mollusken, besonders den Chi- 
tonen, in einigen Hinsichten mehr glichen als jetzt«. 
A testing of this hypothesis on each system of organs will 
however show that a contrary opinion is as well founded as that 
represented by PELSENEER and WIREN, which has been accepted by 
some other modern authors. 
The nervous system differs from that of Chiton, as WIREN 
has pointed out, »durch eine gréssere Tendenz Ganglien zu bilden 
und besonders durch ein immer sehr deutlich entwickeltes Gehirn- 
ganglion« (p. 91). WiREN interprets this fact (in opposition 
to PELSENEER, who finds the Solenogastres in this respect more spe- 
cialized than the Chitons) to signify that »die Solenogastren wenig- 
stens im Besitz eines solchen Ganglions eine mehr primare Eigen- 
schaft als die Chitonen beibehalten hatten«, an opinion which mist 
be considered as fully justified on the same grounds as those 
mentioned by WiREN, and which is corroborated by the conditions in 
Gymnomenia, as well as in Neomenia and Chaetoderma. 
Also with regard to the general arrangement of the genital 
ducts, it must be admitted as probable (with Wrén) that the 
above-mentioned Solenogastres have remained in a more primitive 
stage of development than the Chitons; it should however be ob- 
