36 Sigurd Johnsen. 
northgoing branches but in the eastern basin keeping exclusively 
along the coast of Africa, Palestine and Asia minor. 
Most of the Myctophids of the Mediterranean have their 
main distribution in the western basin. The occurrence in the 
eastern basin of some of them may be explained by the currents 
of the present time; not so with M. glaciale Which is wanting 
here but appears again in the Sea of Marmara. 
From the charts published by Nielsen (l.c. pl. XD), showing 
the salinity at different depths, it is evident that the areas inha- 
bited by M. glaciale, viz. the western basin (especially the Spa- 
nish-African portion of this) and the Sea of Marmora, are identical 
in this respect and show with regard to salinity the same relatively 
low values not found elsewhere in the Mediterranean, while the 
eastern basin and the Ægean have the highest values. I shall 
further bring to mind that acc. to Tåning the stock ot Marmora 
differs in some respects from the Mediterranean race proper: The 
size is on the whole smaller. The number of vertebræ smaller 
(34,460 as against 34,960). The number and the arrangement 
of the photophores are the same but I note that the form exhibits 
a remarkably high percentage of individuals with difference in 
AO between right and left side (31.4 % against 18.1 % in the 
Mediterranean and 14.5 °/o in the Atlantic. Taning J. ¢. p. 36). 
Tåning (2.c. p. 35) remarks further that while abnormities in 
the structure of the spinal column very rarely were met with in 
the Atlantic and the Mediterranean specimens, there were frequent 
instances of these in the material from the Sea of Marmora. 
‘Abnormal short vertebræ may occur among the normal ones, 
or the spinal column may be curved sideways in one or two 
places, or upward and down”. 
From the facts set forth above it must be concluded that 
M. glaciale has a discontinuous range in the Mediterranean seas. 
Once in the past the species must have had a continuous distri- 
bution throughout the Mediterranean. As already mentioned 
I think that M. glaciale entered the Mediterranean waters once 
during the Glacial Epoch when the. hydrographical conditions 
were much the same as those of the boreal Atlantic at present. 
In the following period when changes in the hydrography took 
place, a gradual rise in the salinity and the temperature, M. glaciale 
adapted itself to the new conditions, the dwari-race M. glaciale 
