68 Nils Hj. Odhner. 
and this may be considered as the more primitive condition. If we 
assume that the frontal part of the head of the Solenogastre has 
originated by an invagination of the sensory portion into the oral 
cavity, we shall understand the difference between the two groups. 
Eyes under such circumstances become suppressed and the nerves 
from the cerebral ganglia are directed downwards instead of super. 
ficially. It is probable that in the three pairs of nerves, which issue 
from the brain of a Neomenia, are to be found the homologa of, at 
least, tentacular and labial nerves of the Archiannelids as well as 
of the Gastropoda. 
This homologisation seems to be supported by the opinion ex- 
pressed by THIELE and accepted by HEATH (I. c. p. 167) viz. that 
the cirrose area is homologous with the Chifon snout; this latter, in 
turn, is comparable with the tentacles of the Polychaeta, as is also 
THIELE’S opinion (1902, p. 442). . 
It may be questioned whether the cirrose area has its homologon 
in the oral shield of Chaetoderma, as HEATH (1. c. p. 167) believes. 
It seems more probable that the former corresponds to some part 
dorsally of the pharynx in Chaetoderma, seeing that the oral shield 
occupies a position beneath the mouth. The latter, probably, is a 
character peculiar to Chaetoderma and without correspondence in 
Neomeniina. To this question we shall revert in the sequel. 
The most fundamental difference, however, between Soleno- 
gastres and Archiannelids is displayed in the segmentation of the 
latter. This segmentation, it is true, is merely internal, leaving the 
external body sheath in the shape of an undivided muscular tude, 
and in this respect there is full agreement with the Solenogastres. 
But the internal segmentation is complete, so that the coelom is 
divided into a series of closed chambers without communication 
with each other. | 
As to the segmentation of the Neomeniina WIREN calls atten- 
tion to the fact that there is no correspondence between that of the 
genital tubes and that of the intestine. He arrives at the conclusion 
that it is very different from that of the Annelids, and that it is prob- 
ably no primitive character of the Solenogastres. This discre- 
pancy seems to be of a fundamental importance for a study of the 
affinities between the two groups. 
WirEN compares the Solenogastres with the Annelids, and — 
makes the following statement (1. c. p. 93): »In dem urspriinglichen — 
Bau der Geschlechtsorgane und ihrer Ausfiihrungsgånge bei den 
