os f nm + e . 
rena ee ae i , 4 i . 
. rte c eae OES 
NO  Euphyllopoda Kore pea sie a9 


af *« 
: je 
lees ‘This seems to indicate that the hatching of the nauplius (metanauplius) does 
__ not take place in this vicinity much before the middle of June, even if the spring 
_ comes so early as was the case in 1916. | 
/ 


HIBERNATION 
From the above, it will appear that this species, perhaps to a still greater 
degree than Branchinecta paludosa is exceedingly erratic in its occurrence, for 
I succeeded in finding it only in a few large ponds and lakes, though looking 
for it everywhere during three years. Nor is it known definitely whether any 
of the grown up animals hibernate in deeper lakes, or all die in the fall. Accord- 
ing to Sars (1896, p. 82), however, it is found, in Norway, mainly in rather deep 
_ mountain-lakes; so we may perhaps suppose, that wherever the lake in which 
they occur is deep enough so as not to freeze to the bottom, some individuals 
hibernate there.! I have formerly (1911) expressed this opinion with reference 
to their occurrence in East-Greenland; and the large specimen from St. Paul 
Island, Alaska, secured in March, 1911, seems to point conclusively to this, if 
the collecting date is rightly given. On the arctic coast of this continent the 
species has not yet been found in deeper lakes, though the latter have been only: 
little investigated; the occurrence, however, particularly at Point Barrow (see © 
p- 7) in July, of specimens up to 23 mm. long, seems to make it impossible 
that the oldest (say above 10 mm. long) of these can have attained such a size 
during the little more than a month which has passed since the eggs hatched. 
It is a well known fact, illustrated also by the measurements of the specimens 
given on pp. 4-8, that there is often a great difference in size between the 
Lepidurus occurring together at a particular date in the same pond or lake. 
‘The specimens from Northumberland island, Northwest Greenland, August 7, 
1901 (see p. 5); from Point Barrow, Alaska, July 21, 1882 (see p. 7), and from 
Martin point, Alaska, July 26,1914 (p. 7), are cases in point. Even allowing 
(see above) for a certain number of those occurring during the summer being 
hibernating females, the fact that all intermediate sizes between the smallest 
and the largest individuals are found, seems to prove that the eggs do not all 
hatch simultaneously when the ice melts in the spring, and that the rate of 
growth of the members of the new brood is different, according to the amount of 
food each one is able to secure.” 
According to Scharff (History of European Fauna, London, 1899, pp. 94, 
167) and Wesenberg-Lund (1895) this species is known from arctic, pleistocene 
strata in Scotland and Denmark, as also in southern Sweden (Nathorst.) 

1 Prof. Sars tells me in a recent letter that he thinks this is not improbable. He also informs me that 
_ besides the lakes given in ‘‘Fauna Norvegica’’ it has later been found at many other places in southern 
“ Norway, but only in mountain lakes situated at high elevation (about 2000 to 4000 feet; see also Sars, 
1891, p. 27.) Olofsson’s statements (1918) about its biology in Spitsbergen, outside the summer-months, 
are not founded upon actual observations. 
*'To make these points more clear I have recently taken the trouble to measure the approximate 
lengths (to end of telson) of all the specimens from Greenland and Eurasia (found in the museums in London, 
Copenhagen, Christiania, Uppsala, Stockholm and Gothenburg) which have definite dates of collecting 
given upon their labels. The following is a summary of the results of this, to which should be added the 
(very little) information given by various authors. 
West Greenland. Beginning of July: 5-15 mm. Middle and End of July: 10-23 mm. 
West Greenland. Beginning and Middle of August: 15-30 mm. webs 
ae North Greenland. Beginning of July: 10 mm.; Middle and End of July: 10-20 mm.; Beginning of August: 
-23 mm. 
East Greenland. Middle of June: 1mm.; End of June: 13 and 5-10 mm.; Beginning of July: 10-15 mm.; 
Middle of July: 5-15 mm.; End of July: 3-25 mm.; Beginning of August: 10-25 mm.; Middle of August: 
10-25 mm.; End of August and Beginning of September: 10-30 mm. 
Iceland. Beginning of August: 5-15 mm.; End of August: 25-35 mm. 
Spitsbergen. Beginning of August: 5-15 mm.; Middle of August: 7-23 mm.; End of August: 8-20 mm. 
Baeren island. Middle of July: 10 mm.; End of July: 10-20 mm.; Middle of August: 8-14 mm. 
Norway and Sweden. Middle of July:15mm.; End of July: 5-20mm.; Beginning of August: 10-20 mm.; 
End of August: 25 mm. 
. Novaja Zembla. End of June: 14 mm.; Middle of July: 7-10 mm. 
Siberia. End of August: 15 mm.; Beginning of September: 30 mm. 
