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SECTIONAL TRANSACTIONS.—D. 383 
SECTION D.—ZOOLOGY. 
Thursday, September 5. 
PRESIDENTIAL ApprEss by Prof. F. BaLrour-BROwNE, on The species 
problem (10.0). (See p. 63). 
Mr. F. Leney.—The zoological collections of the Norwich Museum 
(11.0). 
Prof. C. M. Yoncr.—Mode of life and symbiosis in the Tridacnide 
(11.20). 
The family Tridacnide is composed of the two genera Tridacna and 
Hippopus. ‘The former includes a variety of species some of which, in- 
cluding the Giant Clam, TJ. derasa, the largest of all bivalves, are un- 
attached in adult life, resting, hinge undermost, on the surface of reefs. 
Other species of T7idacna bore into rock, but in a different manner from any 
other bivalve ; in these the byssus is retained throughout life. Hippopus 
hippopus lives unattached on the surface of reefs. 
The mantle edges are greatly enlarged, especially in all species of Tridacna. 
In this are immense numbers of zooxanthellz of about thesame size as those 
occurring in corals but differing from these in important details. ‘They 
invariably occur enclosed in blood cells within blood sinuses. ‘The mantle 
edges are curled back over the edge of the shell, affording the maximum 
of light for the alge within. The so-called ‘ eyes’ in the mantle increase 
the effective light-receptive surface. The digestive diverticula are much 
reduced in number, and around those that remain are immense numbers of 
blood cells containing zooxanthellz in all stages of digestion. 
The Tridacnidz have been profoundly modified owing to their as- 
sociation with zooxanthelle, which they literally ‘ farm ’ in the mantle edges 
and later consume. ‘The twisting of the mantle in relation to the body mass, 
which has given rise to extensive controversy in the past, is the direct 
result of this association. 
Mr. H. Ramace.—The spectrographic analysis of animal tissues (12.0). 
Considerable use has been made of spectrographic analysis in the past 
ten years for the detection and estimation of the mineral constituents of 
tissues. Much new knowledge has been gained, and a new field of work 
_ has been opened up. Arc and spark spectra provide very sensitive tests 
for most of the elements, but the oxy-coal gas flame method is sufficiently 
_ sensitive for the detection of almost all the metals usually found in tissues 
and it gives, in less time and in one operation, more accurate quantitative 
results. By its means the specific composition of tissues and organs has 
been determined, and changes in composition during life have been 
followed in ways hitherto scarcely possible by the laborious processes of 
chemical analysis which only were available. 
Dr. G. S. Carter and Mr. J. A. H. Manper.—The flight of the flying- 
fish, Exoceetus (12.30). 
_ A description of the flight is given, and its function as an escape reaction 
in which the fish makes use of refraction at the surface of the water to 
_ €scape a pursuer below the surface is discussed. 
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