20 Sigurd Johnsen. 
the Atlantic plankton is prospering. The plankton is drifting 
with the current and arrives at the Norwegian Sea at a time 
when the hydrographical conditions come nearest to those of 
the Atlantic and the boreal plankton has its season. Instead of 
saying that the fish are driven away from their home in the 
Atlantic it is, I think, more correct to say that they have been 
tempted by the Gulf Stream to make a push northwards, extending 
their distribution in this direction according to their various 
ability of adjustment. That some specimens, when the winter 
comes, are found dead or helpless in the coastal waters can not 
be taken as a disproof hereof as the stranding may be due to 
special causes; these circumstances I have more fully discussed 
in my paper mentioned above. 
With regard to the species here considered I shall add the 
following remarks. 
M. glaciale feeds on plankton crustaceans; it must be con- 
sidered as a good swimmer, at all events there is no plausible 
reason for assuming that this species should succumb to the 
mechanical effects of the Gulf Stream more than do the other 
Myctophids of the Atlantic west of Ireland. According to Holt 
& Byrne (1911 p. 20) M. punctatum and M. crocodilum are 
the commonest Myctophids of the Irish Atlantic slope next to 
M. glaciale. Of these ‘two species M. punctatum has been 
recorded once from Iceland, a stranded specimen (Scopelus ca- 
ninianus of Semundsson 1908 p. 98) and probably also once 
from Hardangerfjord, Norway (Collett 1875 p. 154). Otter- 
strom (1914 II. p. 188) mentions one specimen from Denmark; | 
it has probably found its way thither through the English Channel. 
The northern occurrence of M. glaciale might, however, be 
due to a transport of young stages by the current. Up to a 
certain stage the young-fish of the Myctophids are dependent on 
the movements of the surroundings. In some species as for instance 
M. glaciale and M. crocodilum the larval stages are endowed 
with a dorsal sinus, probably acting as a floater. When the 
northern range of the Myctophidæ of the Eastern Atlantic is different 
this is rather due to differences in their biology (e. g. toleration 
of temperature) than to differences in power of locomotion or in 
transport of the young. If the specimens of the Norwegian Sea 
had drifted with the Gulf Stream from the Atlantic, it is remark- 
