Remarks on Myctophum glaciale (Reinh.). 33 
The only difference is that 7 + 5 and 5+ 8 are not repre- 
sented in the Atlantic, nor 7 + 7 in the Norwegian material. 
It may perhaps be said that in the northern specimens the 
unsymmetrical combinations are more dominant and the combina- 
tion 6 + 7 proportionately less frequent than in the Atlantic 
material; there seems to be a tendency to this when judging from 
the present data but a definite statement requires more and better- 
preserved material. Thus when AO ant. is symmetrical but 
AO post. asymmetrical. e. g. 5 + 7, 5 + 8, the absence of the 
last photophore on the one side of the body may be due to 
damage. On the other hand it is probable that a species at the 
outer boundary of its distribution may exhibit some irregularity. 
It is moreover noteworthy that Taning (1918 p. 36) remarks of 
the Mediterranean race, that a difference between right and left 
side was more strongly marked in the isolated Mormora stock 
than in the race proper. 
M. glaciale exhibits a very remarkable horizontal distribution; 
in explanation hereof | shall venture the following remarks. 
As mentioned veiore M. glaciale ranges in the western At- 
lantic from abt. 35° N. to West-Greenland, in the eastern Atlantic 
from abt. 40° N. to Iceland, the Norwegian Sea, coast of Norway 
to the Spitzbergen waters. A special race inhabits the Mediterranean; 
outside Gibraltar only a few specimens are known from the coast 
of Portugal, probably belonging to the Mediterranean race. The 
species has thus a discontinuous distribution. Ina time 
not too for back the two areas must have been connected. This, 
I think, took place during the Glacial Age. M. glaciale thus 
would be a relict form in the Mediterranean, having developed 
into a special race since the separation from the Atlantic stock. 
From the Scandinavian waters the theory of Glacial relicts has 
been applied on Arctic and Sub-Arctic species of fish and inverte- 
brates which have a main area of distribution in Polar waters and 
another centre of distribution say in the western Baltic, but are want- 
ing or are sparsely found along the Norwegian coast. At the period 
when the Arctic waters penetrated farther south than at present 
the boundaries of the temperate (or boreal) region likewise must 
have been displaced, establishing a connection with the Mediter- 
