24 Sigurd Johnsen. 
the Hebrides (59° 28' N., 8° W.): 25 specimens from 13 to 
16 mm., maximum at 15 mm. (Bg. M.). 
The larger specimens of the “Michael Sars” collections from 
1910 are opportioned into two distinct size-groups, one with 
lengths from 24 to 36 mm. (group I) and another from 45 to 
61 mm. (group II). The eight large specimens collected in 1913 
by the “Armauer Hansen” fall within these two groups. 
The size-groups shown in the graph most probably represent 
year-groups. The expeditions mentioned, it must be admitted, 
worked only during late spring and summer. From the Irish 
Atlantic slope we have, however, the investigations of the “Helga” 
carried out in the months of February, May, July, August, Sep- 
tember and November during the years 1905—1907. This material 
has not been worked out in detail, but Holt & Byrne (1911 
p. 17—18) have published a list of captures where the minimum 
and maximum sizes of the specimens are stated. Larval stages, 
5—10 mm., are only mentioned in catches from May’). [E. g. 
yo. R. 224; 12-V-05. Many larvae, 5—10 mm. (STEG 
20-V-05, many larvae 5—10 mm. S. R. 337, 12-13-V-06. Many 
Scopelus larvae (probably S. glacialis”)|. 
When the Irish records are taken into consideration together 
with the distinct size-groups shown by the material of the said 
two expeditions I think it may be safe to conclude that in the 
Atlantic M. glaciale spawns only once a year — in spring; the 
data further tend to show that the species’ progress of life is on 
an average much the same every year. 
In the Mediterranean, on the other hand, the spawning takes 
place chiefly in winter and spring but in all probability also to 
a certain extent all the year round. (Tåning 1918 p. 43). 
In the Atlantic the species probably attains maturity when 
two years old (group II). Certainly we have no investigations 
into this question, but I base my conclusion on a secondary 
sexual character exhibited in M. glaciale (and other Myctophum- 
species) viz. the precaudal luminous plates, situated infracaudally 
in females, supracaudally in males. Holt & Byrne (1911 p. 14) 
remark that in the specimens examined by them the ventral plates 
1) Some few larval stages seem to occur together with postlarval stages | 
(larger than 10 mm.) in the catches from July and August. 
