Euphyllopoda G 9 



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 greatei 

 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 ISTorway, 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 meithat 

 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. 



2 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. 



North Greenland. Beginningof July; 10mm.; MiddleandEndof July; 10-20 mm.; Beginning of August; 

 8-23 mm. 



East Greenland. Middle of June: 1 mm.; End of June: IJ 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. 



N orway and Sweden. Middleof July: 15 mm.; Endofjuly: 5-20mm.; Beginningof August; 10-20 mm.: 

 End of August: 25 mm. 



Novaja Zemhla. End of June: \\ mm.; Middle of July ; 7-10 mm. 



Siberia. End of August: 15 mm.; Beginning of September: 30 mm. 



