766 SUMMARY OF CURRENT RESEARCHES RELATING TO 



In this way we can easily explain the differentiation of most 

 pelagic species, with the exception of Leptodora hyalina and Byiho- 

 trejphes longimanus, which are not related to the other fresh-water 

 species, and for which we must, therefore, seek a marine origin. 

 Bythotrephes would be derived from an ancestor which was common 

 to it aud to Podon, its nearest ally. Leptodora, on the contrary, 

 according to Weismann's view, would have branched off from a 

 primaeval Daphnid, of whose direct descendants nothing further is 

 known. 



But how could the passage from salt to fresh water be effected ? 

 Pavesi supposes the closing of a fjord, and its gradual conversion 

 into a fresh-water lake. This is possible ; but for the definite deci- 

 sion of the question we have still no reliable materials. So soon, 

 however, as the adaptation to fresh water had been effected, the dis- 

 tribution of these forms of marine origin took place in the same way 

 as with other pelagic fresh-water forms, and thus these two forms 

 would be introduced into lakes which were never in direct communi- 

 cation with the sea. 



Professor H. N. Moseley also delivered an address * on " Pelagic 

 Life " (Fauna and Flora), at the Southampton Meeting of the British 

 Association, which constitutes a highly interesting summary of our 

 existing knowledge on the subject. 



Mollusca. 



Curious Secretion in Gasteropods. — The parts termed salivary 

 glands in prosobranchiate gasteropods are far from being sufficiently 

 understood ; they offer a tempting subject of research to young in- 

 vestigators. In particular is this the case with Dolium galea, the 

 largest gasteropod of the Mediterranean. Poli was the first to notice 

 the oesophageal organs of this mollusc. Keferstein has given an 

 original description and figure of the whole apparatus in Bronn's 

 ' Thier-reich.' Troschel noted the very acid "saliva" of Dolium, in 

 which Boedecker found by analysis a large percentage of S0 4 H 2 . 

 De Luca and Panceri confirmed his results, obtaining more than 3 per 

 cent, of free sulphuric acid. They also observed that much carbonic 

 acid was given off when the freshly excised " glands" were placed in 

 contact with the air, and further showed that other prosobranchs, as 

 well as Aplysia, likewise yielded free sulphuric acid. They especially 

 indicated the enormous size of the " glands " ; in a Dolium whose 

 total weight was 1305 grammes, the shell weighed 550 and the 

 " glands " 150 grammes. Hoppe-Seyler remarks that a secretion so 

 wonderfully composed as that of Dolium has nothing in common with 

 the saliva of the higher animals. Another eminent physiological 

 chemist, Dr. R. Maly,f has lately studied this " saliva " and expresses 

 similar doubts. He finds that, added to alkaline neutral or acid 

 solutions, together with albumen fibrin or starch, it digests none of 

 these substances. Neither could he detect any ferment in the 



* ' Nature,' xxvi. (1882) pp. 559-64. 



t SB. K.K. Akad. Wiss. (Wien), Ixxxi. (1880) p. 376, and Monatsb. f. 

 Cliem., i. pp. 205-15. 



