Remarks on Myctophum glaciale (Reinh.). 37 
var. thori Tåning of the present time being the result of the 
adaptation, as the last phase followed the separation in a western 
and an eastern stock. The extraordinarily high salinity of the 
Mediterranean is due to the extensive evaporation combined with 
the small amount of freshwater which is added by rainfalls and 
rivers. The eastern basin with its maximum of salinity must 
be regarded as the chief centre of evaporation and probably 
always has been somewhat in advance of the other portions oi 
the Mediterranean with regard to salinity and temperature. At 
a certain stage in the salinity M. glaciale var. thori became extinct 
in the eastern basin and gradually retreated northwards finding 
in the Marmora Sea the last place of refuge. 
As mentioned above (p. 36) the stock of Marmora differs in 
some respects from the Mediterranean race proper. Some of these 
features evidently are abnormal ones which must be taken in 
connection with the isolation of a relatively small stock living 
under difficult circumstances. Within the small area represented 
by the Sea of Marmora the hydrographical conditions vary very 
much; in the southern part, where M. glaciale occurs, there is 
an inflow of Mediterranean water, while, from the north, brackish 
water from the Black Sea comes in as a surface current through 
the Bosphorus. (Nielsen 1912 p. 112 et seg.). On the other 
hand the specimens from the Marmora have on the average 
a smaller number of vertebre than the Mediterranean race and 
the size seems to be somewhat less; in other words the reduction 
is here farther increased than in the western Mediterranean. This 
has probably not taken place since the isolation of the stock in 
the Marmora. The view might however be maintained that the 
Separation in a western and an eastern stock had taken place at 
an earlier date than here presumed and that the western race 
thori and the Marmora variety are the results of convergent 
adaptation of the two stocks of M. glaciale. With regard to 
photophores the specimens from Marmora do not differ from 
those of western Mediterranean and for this reason Taning 
does not classify them as a special race. For the same reason 
I think that the eastern stock became separated from the western 
one at a time when the race thori was established in its main 
features, but, as the eastern basin during the hydrographical 
changes was in advance with regard to the rise in salinity and 
