Geological Societtj. 375 



crater, a phsenomenon which, in a greateror less degree, is at all times 

 observable. The author descended twice into the interior of the crater, 

 which then presented a comparatively level surface j its sides con- 

 sisting of strata of loose volcanic sand and rapilli, coated with saline 

 incrustations of common salt, coloured red and yellow by peroxide of 

 iron. The vapours which issued from various parts of the surface, 

 collected and condensed by means of an alembic introduced into the 

 ground, were found to consist principally of steam and muriatic acid, 

 with only a slight trace of sulphureous or sulphuric acids. From a 

 trial with solution of barytes, the author concludes that carbonic acid 

 was also exhaled, but neither nitrogen nor sulphuretted hydrogen 

 appeared to form any part of the gas emitted. The steam issuing 

 from the lava contained both free muriatic acid and also muriate of 

 ammonia, which latter salt could not be detected in the gas from the 

 volcano itself. The author conceives that these volatile principles 

 are entangled in the lava, and are subsequently disengaged. 



March 26. — " On the Temperature of some Fishes of the Genus 

 Thynnus." By John Davy, M.D., F.R.S., Assistant Inspector of Army 

 Hospitals. 



Tlie author had occasion to observe, many years ago, that the Bonito 

 [Thynnus pelamys, Cuv.) had a temperature of 99^ of Fahr. when the 

 surrounding medium was80°-5, and that it, therefore, constituted an ex- 

 ception to the generally received rule that fishes are universally cold- 

 blooded*. Having found that the gills of the common Thunny of the Me- 

 diterranean {Thynnus vulgaris, Cuv.) were supplied with nerves of un- 

 usual magnitude, that the heart of this latter fish was very powerful, 

 and that its muscles were of a dark red colour, he was led to conjec- 

 ture that it might, like the Bonito, be also warm-blooded ; and this 

 opinion is corroborated by the testimony of several intelligent fisher- 

 men. The author endeavours to extend this analogy to other species 

 of the same family, which, according to the reports of the fishermen 

 of whom he made inquiries, have a high temperature, and in whose 

 internal structure he noticed similar peculiarities as in the Thunny ; 

 namely, very large branchial nerves, furnished with ganglia of consi- 

 derable size. In this respect he considers that in these fishes the 

 branchial system of organs makes an approximation to the respiratory 

 apparatus of the Mammalia, and that it probably contributes to the 

 elevation of temperature, resulting from the more energetic respira- 

 tion which he supposes to be exercised by these organs. He, how- 

 ever, thinks it not improbable that these fish may possess means of 

 generating heat peculiar to themselves, and of which at present we 

 have no adequate idea. He conceives that the situation of the kid- 

 neys, of which a considerable portion is even higher than the stomach, 

 and posterior to the gills, and which are of large size, and well sup- 

 plied with nerves and blood-vessels, may possibly act a part in the 

 production of an elevated temperature ; but, on the whole, he is dis- 

 posed to ascribe the greatest share of this effect to the superior mag- 

 nitude of the branchial nerves. 



* See Mr. Brayley's paper on the Distribution of the Powers of pro- 

 ducing Heat and Light among Animals, in our last Number, p. 245. 



