Miscellaneous. 315 



MISCELLANEOUS. 



Researches upon the Defensive Glands of Bombardier Beetles. 



By Fr. DlERCKX. 



In a note published in the ' Comptes Rendus ' of January 23, 

 1899, Mons. L. Bordas describes the anal gland of Carabus nemo- 

 ralis, Illig. For a long time past we have studied the same organ 

 in a considerable number of species, and we have arrived at results 

 that do not always agree with those of M. Bordas. We have there- 

 fore thought t useful to introduce a few critical observations into 

 the description of an allied type, which in many respects is more 

 interesting. 



Since the species of Brachynus present a strong contrast to the 

 rest of the Carabidoe, owing to the faculty which the various species 

 possess of projecting, with crepitation and the formation of a con- 

 spicuous puff of vapour, the secretory product of their anal glands, 

 let us seek to determine the conditions of this phenomenon. 



I. Anatomy. — In Brachynus crepitans, L., the glandular apparatus 

 is double and situated, as in the other Carabidae, on both sides of 

 the rectum. Each element is composed of a secreting portion, a 

 collecting-duct, and a reservoir. 



A. Secretory lobes. — Each cylindrical lobe of the aciniform gland 

 is traversed by a duct with a cuticular wall strewn with little 

 nuclei. Between this axial duct and the enveloping propria lie the 

 active cells, each enclosing, besides the nucleus, a radiated pyriform 

 vesicle, drained by a canaliculate filament. M. Bordas does not 

 mention this intracellular vesicle in the case of Carabus nemoralis ; 

 we have observed it in all the species examined, with modifications 

 interesting from the point of view of taxonomy. 



B. Collecting-duct. — This is from 25 to 30 miUim. in length in 

 the case of Brachynus, and is constituted by two tubes which fit 

 one into the other, the innermost of which is kept wide open by 

 means of a series of hyaline cuticular disks, which are set more or less 

 close together from one end of the duct to the other. Excluding 

 the propria, there is only a single layer of cells ; the axial tube 

 which is enclosed therefore results cytologically from the cells of 

 the outer wall, where the nuclei are always ensconced. The species 

 of Carabus have the disks merely outlined, and the tube does not 

 possess a double wall. In Panaga^us the outline of the disks has 

 entirely disappeared. From this simpler condition to the more 

 complex forms the differentiation of the cells varies greatly ; but in 

 no species have we met with a wall consisting of several layers of 

 cells. We do not know how M. Bordas was able to detect in this 

 sti'ucture, in the case of Carabus nemorcdis, two muscular coats and 

 an internal epithelium with flattened cells. 



C. Reservoir. — This is in the shape of a wallet with the convex 

 side towards the axis of the body. The collecting-duct opens in the 



