ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 441 



Arthropoda. 



a. Insecta. 



Detonating Organ of Brachinus crepitans.* — Professor P. de 

 Roiigemont gives a careful description of the anatomy and physiology 

 of this organ in the above species of Bombardier beetle. 



He confirms in the main the account given by Leon Dufour, of 

 what that writer terms the "preparing" and "preserving" organs. 

 There is, however, a long, slender, thread-like body on each side, lying 

 between the preparing and preserving organs, which was not fully 

 described by that author ; it is tubular, and twisted in all directions 

 upon itself ; when isolated and unrolled it measures from 45 to 50 mm. 

 in length, and has the uniform width of a fine hair ; it does not 

 branch at all except where it is attached to the preparing organ, where 

 it bifurcates, each branch entering one half of a double glandular organ. 

 The glands are strictly anal glands ; their excretory tubes, just 

 mentioned, appear under the Microscope to be filled with bead-like 

 globules of air ; the vacant spaces which are sometimes noticed 

 in them are occupied by air which is pushed forward. The tube 

 I'eally contains an inner central straight, and an outer spiral tube 

 coiled round the former ; it is this latter which generally alone con- 

 tains the air. The colour of the whole is whitish ; the external coat 

 is muscular and abundantly supplied with trachea, the lining mem- 

 brane consists of connective tissue containing about a dozen vesicles. 

 The air may be released under water by puncturing the tube, and 

 then takes the form of bubbles, whose volume is greater than that of 

 the cavity of the tube itself. 



The preparing organ, which Professor de Eougemont prefers 

 to call " condenser," opens into the reservoir or preserving organ. 

 Some of the vapour produced by the detonation was obtained by 

 placing forty specimens in alcohol, weakened by the addition of 

 one-third of water ; soon after, single detonations occurred and vapour 

 was sent up ; in five minutes from immersion a rapid fire of explosions 

 took place, and then the movement slackening they became less 

 frequent, concluding with a volume of bubbles after death, probably 

 owing to the relaxation at that moment of the sphincter muscle of the 

 reservoir. Analyses made by Professor Billiter show the composition 

 of the vapour to be : — oxygen, 73 • 1 ; carbonic acid, 20 • 6 ; nitrogen, 

 6*3. This large proportion of oxygen is sufficient to rekindle a 

 smouldering match. 



The preserving organs or reservoirs, lying behind the condensers, 

 have a brown chitinous colour, and enclose a brown liquid containing 

 minute, flat, brownish, hexagonal crystals ; it has not been found pos- 

 sible to analyze it, but it would appear by analogy with similar 

 substances found in Carabus niger and auratus, to consist of butyric 

 acid. Its origin is doubtful, and it plays no part in the production of 

 the explosion, but gives out a strong odour when expelled by that 

 process ; it produces a brown patch on glass, under which the explosion 



* MT. Schweiz. ETitom. Ges., vi. (ISSI) pp. 99-10.^. 



