Rotifera of the Family Asplanchnidte. 37 



Rabot, able to indicate the existence of A. helvetica under the 

 Arctic circle, at a higher latitude than that of the lakes inves- 

 tigated by Nordqvist. It abounds in the Imandra and in the 

 Kolozero (Russian Lapland, 68° N. lat.), where M. Ilabot has 

 taken it in considerable quantities, especially in the second 

 locality, on the 16th August, 1885, between 8 and 9 o'clock 

 in the evening, at the surface. These sheets of water, pro- 

 bably the remains of an ancient strait, are about 100 metres 

 above the level of the sea, under the isotherm of 0" C * 



In this connexion it is of interest to remember tliat A. hel- 

 vetica was collected by Imhof in Switzerland up to an elevation 

 of about 1800 metres in the lake of Campfer t ; sooner ur later 

 it will certainly be met with close to the limit of perpetual 

 snow. 



The chorological data are much less numerous for the other 

 species. A. Brightuoelli and A. jpriodonta^ long known in 

 England, were met with, twenty years ago, at Brunswick by 

 Eyferth, and more recently by Plate in the neighbourhood of 

 Bonn and Bremen. A. Hieboldi is cited at Wurzburg (Ley- 

 dig) and at Prague (Stein). 



But the most interesting of the Asplanchmv from the point 

 of view of geographical distribution is, unquestionably, 

 A. syrinx. Described by Ehrenberg from specimens collected 

 at Berlin, it has been indicated at St, Petersburg (VVeisse), 

 in Egypt, and at the summit of Adam's Peak (2260 metres) 

 in Ceylon (Schmarda). 



One may, perhaps, be tempted to doubt the accuracy of the 

 determinations of this species, of which, so far as I know, 

 there still exists only the figure published by Ehrenberg in 

 1888. 1 may remark, however, that VVeisse and Schmarda, 

 who were both very well acquainted with the Rotifera, no 

 doubt had Ehrenberg's work before them|. 



* Some zoologists regard light as the priucipal cause of the daily 

 vertical migrations of the pelagic fauna. lu connexion with this I would 

 remark that, in the northern lakes in which this faujia seems to attain its 

 maximum development, the supposed nocturnal or crepuscular animals 

 which constitute it are condemned througiiout the summer to the per- 

 sistent brightness of the long polar days. From the small depth of many 

 of the lakes it is even impossible for them to descend sufficiently to avoid 

 the luminous rays. 



t Imhof, " Ueber die mikroskopisclie Thierwelt hochalpiner Seen " 

 (000-2780 M. u. M.)," in Zool. Auz. 1887, pp. 13 and 33. (Translated 

 in ' Annals,' ser. 5, vol. xix. p. 276.) 



X In noticing the discovery of Hydatina senta in the neighbourhood of 

 Auckland, New Zealand, Schmarda states that he was able to compare 

 the living Rotifera on the spot with the figures of Ehrenberg, whose volu- 

 minous Atlas in folio he had taken with him on his voyage. See "Neue 

 wirbellose Thiere beobachtet uud gesammelt auf einer Reise um die 

 Erde, 18->3 bis 1857 " (1850), vol. i. p. 50. 



