374 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The water contains in solution 0"01 gr. of organic matter per litre. 

 This material is fixed by vegetable organisms, e. g. bacteria, algas, 

 desmids, diatoms, oscillaria, &c. The " aquatic dust " in suspension in 

 the water is absorbed by Protozoa. It is the first stage in the organiza- 

 tion of nutritive material. Larger animals, such as rotifers and Entomos- 

 traca, feed on these plants and animals. Insectivorous fishes feed on these, 

 and carnivorous fishes prey on the last : whilst finally these are eaten by 

 birds and man. The carcases and ejecta of all these forms serve to keep 

 the quantity of organic material constant. 



Microscopic Fauna of High Alpine Lakes.* — Dr. 0. E. Imhof has 

 investigated the fauna of various Alpine lakes at altitudes of from 

 600-2780 metres above the sea ; after a reference to what has been done 

 by previous observers he gives the results of his own studies. The great 

 majority of lakes over 2000 metres harbour a pelagic fauna which is 

 very rich in individuals ; in some a Daplmia was particularly plentiful, 

 and in others Diaptomtis alpinus ; up to 1796 metres (the Silsersee) there 

 were 7-16 species in one lake ; the higher the elevation the smaller the 

 number of species ; Daphma, Cyclops, and Diaptomus were the most widely 

 distributed genera ; Bosmina was found at 1908 m. (Cavloccio) ; Leptodora 

 hyalina was nearly always present up to 1075 m. Anursea longispina was 

 the most generally distributed rotifer, and was found as high as 2640 m. 

 Among the Protozoa Ceratium hrnidinella was widely and generally found 

 as far as 1993 m. Peridinium extends to 2222 m. The Copepod Hetero- 

 cope robusta was found in three lakes in the Upper Engadine. 



MoUusca. 



Growth of the Molluscan Shell.t —According to Reaumur (1709) the 

 growth of the Molluscan shell was due to the mechanical deposition of a 

 secretion. In spite of the objections urged by Mery (1710) and Herissant 

 (1766), who advocated an internal organic growth by intussusception, 

 Reaumur's theory has been virtually accejjted till within the last few years. 

 A vigorous opposition by Nathusius-Konigsborn in 1878, followed up by 

 Tullberg in 1882, and Ehrenbaum in 1884, has done much to elucidate 

 the process. According to Tullberg one portion of the shell grows by 

 apposition, another by the modification of the outer zone of epithelial 

 cells, while Nathusius-Konigsborn maintained that the growth of the 

 shell, though strictly internal, was independent of any cellular element. 

 F. Miiller (1885), on the other hand, was led to conclude that the shell 

 does not grow independently of the cells, while his results were equally 

 conclusive against the possibility of growth by apposition of elements 

 secreted from the mantle. A brief summary of some of the more detailed 

 results of the last two observers is given at the reference noted below. 



Nervous System in Tenioglossate Prosobranchs.i — M. E. L. Bouvier 

 describes certain modifications of the typical strepsineurous arrangement in 

 Prosobranchs, which lead on to a zygoneurous condition. Some of the 

 Melaniidfe and Cerithiidae have a commissure passing directly from the 

 subintestinal ganglion of the visceral loop to the pallial (pleural) ganglion, 

 on the right side. Other members of the group have this connection less 

 perfect. The union between the supra-intestinal and pleural ganglion of 

 the left side is much rarer, but M. Bouvier finds it in Ampullaria, Naiica, 



* Zool. Anzeig., x. (1887) pp. 13-17, 33-42. 



t Naturforscher, xx. (1887) pp. 137-8. 



X Comptes Reudus, civ. (1886) pp. 447-8. Sec also this Journal, 1S8G, p. 584. 



