Miscellaneous. 499 



European lakes, as made known to us by Forel, Lilljeborg, P. E. 

 Miiller, Pavesi, G. O. Sars, Weissrnann, &c. As in the Scandinavian 

 lakes, certain species of Cladocera are represented by a considerable 

 number of individuals. We also find them attacked by parasitic 

 Cryptogamia. Lastly, the presence of numerous Infusoria and of 

 Rotifera of the genus Anurcea increases the analogy of this fauua 

 with that of the Swiss lakes recently explored, from this point of 

 view, by Iinhof. 



"These resemblances are explained by the analogy of the con- 

 ditions of temperature (68° F. at the surface of the Lake of Geneva, 

 according to Forel ; 57°*2-60°*8 F. in the Gulf of Finland, accord- 

 ing to observations made at the same time as the collections). Put 

 they are particularly explained by the slight degree of saltness of 

 the water of the gulf (0-073 per cent, at Croustadt, 0*202 per cent, 

 at Leskar, and 0*751 per cent, between Gothland and the Russian 

 coast). From the point of view of the pelagic fauna we may com- 

 pare the Gulf of Finland to a lake with a wide opening to the 

 Paltic. 



"As to the central basin of that sea as far as 16° E. long, and 

 probably still further, even to the mouth of the Oder, it presents 

 very distinct characters of transition between the pelagic fauna of 

 fresh waters and that of strongly saline waters. Xature seems to 

 have completely realized the conditions which M. Plateau and M. 

 Pert reproduced experimentally in the course of their investigations 

 upon the vitality of Daphnue in waters of different salinity. 



" The presence of Evadne and Podon in the Gulf of Finland shows 

 that the Cladocera of those genera, which are regarded as essentially 

 marine, may adapt themselves to the conditions of existence in 

 scarcely brackish waters. Podon intermedins, for example, which 

 in the Mediterranean bears a salinity or 3*7 to 3*9 per cent., also 

 lives in the eastern part of the Gulf of Finland, where, as has been 

 stated, the water only presents a salinity of 0*073 per cent. We 

 are thus led by the Podon and Evadne of a nearly fresh sea to the 

 lacustrine forms with a marine facies (Bi/lhot replies, Polyphemus, 

 &c), which have been met with in most of the lakes of Europe " *. 

 — Comp>tes Eendus, March 30, 1885, p. 919. 



* [In their concluding remarks the authors assume that the lacustrine 

 Cladocera derived from marine forms must have been introduced by the 

 agency of migratory birds to their freshwater habitats, and therefore from 

 the north to the south. But one does not see why the agency of migra- 

 tory birds should be invoked at all. — W. S. D.] 



