ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
153 
Food of Marine 5 ! Fishes.* — Dr. G. B. De Toni has a useful little 
paper in which he brings together numerous facts and references as to 
the food of marine fishes. 
Winter-Plankton in Large and Small Basins.f — Dr. 0. Zacharias 
raises a very interesting problem by stating in his usual careful manner 
the differences which obtain as to the same species in the winter-plankton 
of large and small water-basins. In the small basins there is a remark- 
able persistence in numerical strength which is not exhibited in the 
large. He shows that it is not a matter of temperature, and he empha- 
sises in passing that in fresh-water plankton light is more important. 
Thus the high productivity in April, as compared with March and 
February, is mainly referable to the increasing intensity of the illumi- 
nation. But how is it that, in spite of the meagre sunshine of November 
and December, there is an almost luxuriant {“fast iippig ”) productivity 
in the planktonic diatoms in small basins ? And on the vegetable 
plankton the animal plankton of course depends. His theory is that 
many algaa are capable of “ amphitrophy,” in other more intelligible 
words, that they are able to feed upon the dissolved organic substances 
in the water, which are naturally more available in the limited area of 
a small basin. 
Fauna of Wadi Natroun.J — Herr J. Dewitz gives an interesting 
account of what he observed during a stay of two months in this valley 
of soda-lakes which lies in the Libyan desert about 170 kilometres from 
Cairo. Grasshoppers, cicadas, bugs, beetles, Planorbis-like shells, Helix 
desertorum , &c. are recorded ; but it is perhaps of most interest to notice 
his remarks on the red waters of the soda-lakes themselves. The redness 
seems to be due to bacteria, but at certain seasons Artemia salina is 
abundantly present. From resident birds and a desert fox he obtained 
various parasitic worms, which probably have arthropods as their 
intermediate hosts, since there are no fishes and only two species of 
molluscs. 
Tunicata. 
The Ascidian Half-Embryo.§ — Mr. H. E. Crampton, jun., finds that 
an isolated blastomere of Molgula manhattensis segments in a strictly 
partial fashion as if it were still a part of an intact embryo. The result 
is a larva of less than normal size, and with certain defects. Later on, 
however, a process of regeneration gradually masks the partial nature 
of the development, and the final result is nearly complete. 
INVEBTEBRATA. 
Mollusca. 
y. Gastropoda. 
Dimorphism in Crepidula.|| — Prof. E. G. Conklin gives examples of 
“ environmental polymorphism ” (a useful phrase) in G. convexa and 
* La Nuova Notarisia, x. (1899) pp. 21-7. 
f Zool. Anzeig., xxii. (1899) pp. 25-31. % Tom. cit , pp. 53-61. 
§ Ann. New York Acad. Sci., x. (1898) pp. 50-7 (2 pis.). 
|| Proc. Acad. Nat. Sci. Philadelphia, 1898, pp. 435-44 (3 pis.). See Amer. Nat. 
xxxiii. (1899) pp. 160-1. 
1899 
M 
