Norwegian Solenogastres. 67 
————r—ÆJÆJ—J— 
be signalized as a rudiment of a radular tooth like that of Chaeto- 
derma. In the same genus a pair of elongated salivary glands 
exist, reminding one vividly of those of certain Solenogastres (for 
instance Dorymenia). They debouch above the cartilaginous sub- 
stance (radula tooth), thus presenting an adapted starting point for 
a development in the direction shown by Pruvor (cf. above). Further, 
Protodrilus is hermaphrodite, Polygordius monosexual, and the ge- 
nital products are formed in the dorsal chambers of the segments. 
The caudal segment carries a pair of appendages and in some 
species a dorsal lobe; the former at the first glance may seem com- 
parable with the gills of Chaetoderma, and also, after division into 
folds with such different types of gills as in Neomenia and Alex- 
andromenia; the dorsal lobe recalls the roof of the cloaca in for 
example Dorymenia and others. The homologon of an anterior pedal 
gland seems to be present in the »glandole emolinfatiche« 
(PIERANTONI). Even a caudal sensory organ may be present, in 
position and structure greatly resembling that of the Solenogastres. 
This comparison — to-which THIELE has previously (1902) 
drawn attention — might perhaps be drawn out in further detail, 
but the conditions mentioned should suffice to show the striking 
agreement. | | 
However betraying the similarity between the Solenogastres and 
the Archiannelids be, there are nevertheless some essential differences 
which show that there can be no question of a direct derivation of 
one of the groups from the other. Thus for instance the circulatory 
and the nervous systems are differently organized, and the Soleno- 
gastres have a cuticula with spicula. Moreover, in the Archianne- 
lids the presence of tentacles, eyes and statocysts signifies a more 
perfect type of organism. To some extent, this difference may be 
explained by the different mode of life; the Archiannelids live freely 
in sand at inconsiderable depths; the Solenogastres, on the other 
hand, are generally tenants of deep water and burrow in 
sand, or feed on Hydroids and Alcyonarians. This mode of life has 
rendered organs of sight superfluous, and instead of them there 
is developed a more perfect sense of feeling, located as a matter of 
course in the mouth region. Here we find perhaps the homologon 
of the tentacles of the Archiannelids in the cirrose area of the 
Neomeniina. In reality the cirrose area in some forms (for instance 
Gymnomenia and Wirenia) is rather sharply separated from the 
oral cavity (cf. also THIELE 1894, p. 286, and HeaTtH 1911, p. 167), 
