iS THB EL, NORTHERN AND ARCTIC INVERTEBRATES. IT. SIPUNCULIDS. 
centage. In all these cases only one retractor-root is present, the second being 
wanting altogether. In four instances the root was attached on the left side of the 
nerve-cord, in the fifth on its right side. According to my experience the failure of 
a retractor in the Sipunculids is not at all such a rarity as one might be disposed 
to believe. ; 
It is a known fact that the presence or absence of hooks behind the tentacles 
does not necessarily signify specific characters. On the contrary, forms are met with 
which are armed with hooks during a period of their life but lose them subsequently. 
In the two forms which I have called Ph. Sabellarie and improvisum, the former is 
unarmed, is smooth externally and has the body-cavity filled up with eggs, while the 
latter is armed with hooks, bears papille externally on the body and is devoid of 
eggs. For reasons given on Pages 21 and 22 and also below (under the several species), 
I am much inelined to believe that these two forms represent different sexes of the 
same species, the former being a female, the latter a male. Supposing that the truth 
of my supposition should be proved beyond doubt, one would have one more proof 
of the fact, that the presence and absence of hooks may sometimes be of but little 
systematic value. Seeing that the hooks are irregularly arranged and not seldom 
absent in Ph. Sarsi also, ineluding all the specimens from the Arctic and Northern 
Seas which I have grouped together under the name ”anceps”', my view on this point 
seems to be confirmed. Of course I am hereby far from wishing to deny their value 
as a whole for the system. Their size, general shape and arrangement must always 
form good criteria for identifying the species. 
Moreover, if it should be confirmed that the two forms mentioned really belong 
to the same species, another question of importance arises. What part dö the papilla 
of the body-wall play in the system? Supposing I am right in my supposition, the 
presence or absence of them must, in several cases, be of questionable value for the 
systematist. 
Phascolosoma abyssorum Koruen and DANIHLSSEN 1875 and 1877. 
PI. V.; Figs. 71—75, Pl. VI. Figs, 76—81; PI. XIV. Fig. 206. 
Habitat: 
West Coast of Norway: Bergenftjord at a depth of 200—300 ims., stony bottom, 
in the canals formed on the Lima excavata by the Cliona abyssorum Sars (Mus. B.) 2 sps. 
Distribution in General: 
According to FiscHER', KÖKENTHAL caught this species at Spitzbergen. If this 
is true, the species may very probably have a wide distribution im the Atlantic and 
Arctic Seas. 
Two types of this rare species have been sent to me for inspection from the 
Bergen Museum. They measure about 38 mm. in length. Distance between anus 
1 Abhandl, aus dem Gebiete der Naturwissenschaften, Hamburg 1895, p. 14, 
