60 Nils Hj. Odhner. 
served that at the distal ends of their coelomoducts the Solenogastres 
show specialization in various ways (development of vesiculae and 
copulatory organs), a fact which signalizes a higher differentiation . 
than in the Chitons, a differentiation which has evidently originated 
from a type more primitive than the Chitonean one. 
The differentiation of the genital ducts, as a whole, exhibits a 
parallel to that of the epidermis, in as much as forms with a simple 
epidermis also show relative primitivity in their genital organs. 
In Nematomenia the latter are histologically more simply constructed 
than in any other Solenogastre, seing that no paired cyanophilous 
part of their distal legs is yet developed. In Wirenia the coelomo- 
ducts are primitive in their entire separation from each other. 
In the intestinal canal, too, we find a progression from simpler 
to more complicated conditions. Thus in Nematomenia the intestine 
is straight, without diverticula, whereas the latter are developed in 
the most other forms. Gymmnomenia has a few and only weak ones, 
while in Simrothiella and specially Neomenia and Proneomenia 
they are very numerous and well developed. Here they appear as 
long fissure-like projections from the lateral sides of the intestine, 
occupying its whole extent. A further specialization of this state is 
met with, for instance, in Drepanomenia, where the diverticula re- 
present small closed coeca each opening with a circular hole. 
On the other hand the pharyngeal region shows differentiation 
independent of the general habitus of the animal. Thus a proboscis 
is present in such different types as Nematomenia banyulensis, Dre- 
panomenia vampyrella and Neomenia, whereas it is absent, for in- 
stance, in Proneomenia and Alexandromenia. In the two first- 
named genera the proboscis is invaginable out from its base; in 
Gymnomenia, on the other hand, it can be involved from its apex. 
Thus we find, in the Solenogastres, differentiations in the same 
directions as among the Gastropoda and independent of the orga- 
nization in general. 
As to the circulatory organs, they are so intimately combined 
with the respiratory ones that they must be dealt with simultane- 
ously. In the organization of the breathing organs the Soleno- 
gastres obviously represent a lower type than the Chitons. As, 
however, the development of gills is closely connected with the for- 
mation of a mantle cavity, it is most convenient to consider all 
these organs in connection with one another. 
WirEN (1894) deals with this problem. He prefaces the dis- 
