414 RECORD OF CURRENT RESEARCHES RELATING TO 



development ; e. g., they multiply in the lakes of Brianza and Endine, 

 whicli are only 10 metres deep. Some forms, as Bythotrephea, are 

 found only in the deepest lakes. As to the bathymetrical limits of the 

 fauna, Leptodora lives generally, by day, at about 15 metres depth. 

 At 10 and 30 metres it is generally rare, though in some cases it has 

 been found even at 100 metres, and in shallow lakes is common at 

 5 metres. Daphiia cristata of Lake Idro is common at 5 to 15 

 metres, very rare at 50 metres. Daphnia magna is most abundant at 

 30 to 50 metres. On stormy days few forms were found at 5 metres 

 depth. The almost absolute absence of Crustacea in the Lake of 

 Garda, at 5 metres even in calm weather, is attributed to the great 

 transparency of the water. 



Professor Pavesi thinks the influence of temperature nil or inap- 

 preciable. He assigns a marine origin to the fauna in question ; 

 fiords changed to lakes, part of the isolated species dying out, others 

 becoming adapted to new conditions of life, diffusion of these forms, 

 by various means of transport, to neighbouring lakes of difiierent 

 epoch and origin, such as the lakes of Switzerland, Bavaria, and Lake 

 Trasimeno. This confirms Stoppani's theory of the origin of the lakes 

 in Upper Italy. 



MoUusea. 



Development of the Pulmonate Gasteropoda.* — M. Fol com- 

 mences with an account of the time and mode of oviposition in these 

 creatures. The genus Planorhis seems to have eggs best adapted for 

 investigation ; the author found their eggs in the environs of Geneva, 

 during the months of May and June ; those of the small P. contortus 

 were found on the lower surface of dead leaves in small ponds. From 

 July to September P. marginatus deposits its eggs very largely on the 

 leaves of the water-lilies at the edge of marshes ; eggs of Ancylns 

 fluviatilis are to be found under the stones of the bed of streamlets, 

 and those of A. lamstris on the leaves and branches of the water-lilies. 

 Those are best studied that are found in completely natural positions. 

 For the terrestrial Pulmonata, the author used Helix, Avion, and 

 Limax; after a shower the spots where the snails are seen making 

 holes in the ground should be carefully marked, but the eggs 

 should not be sought for till the succeeding day, when they will 

 certainly be found. H. pomatia lays its eggs in June and July. 

 The hard shell of the eggs of H. hortensis seems to offer an in- 

 superable objection to their examination. Limax has very trans- 

 parent eggs. L. agrestis lays a large number, at the commencement 

 of winter, around the roots of lettuces in market gardens, but the 

 larvae are too opaque and their rotation is too rapid for useful examina- 

 tion. L. maximus var. cellarius is very favourable ; its eggs are found 

 from September to November in damp spots, and under boards which 

 have been some time on the ground. 



Methods of Investigation. — These were of two kinds, by means of 

 living specimens, and by means of sections ; the former were com- 

 pressed by the compressorium, of which M. Fol gave an account in 

 * 'Arch. Zool. exper. et gen. (Lacaze-Duthiers), viii. (1880) p. 103. 



