BEETLES. 



393 



FIG. 474. Halt- 

 plus fasciatus. 



and North America. The species of Affabus, Mat us, and Ilybins are all somewhat 

 similar in appearance to Rhantus, and most of the species are about the same size. 

 Coptotomus interrogatus is very common in the eastern United States. It is about 

 0.35 of an inch long, the elytra are somewhat irregularly striped longi- 

 tudinally with yellow, and the prothorax is banded transversely with 

 the same color. 



In Hydroporus, a genus which contains over seventy-five described 

 North American species, the prosternum is deflexed between the front FIG. 473. Jii/,/r,,. 



, . , ,, . , , . . , , porusrotundatus. 



coxae, the anterior and middle tarsi are apparently four-jointed, the 



scutellum is not visible, and the metasternum attains the mesosternum. 

 The species are all of comparatively small size. 



The family HALIPLID^:, often united with the Dytiscidas, includes a 

 small number of minute, sub-aquatic Coleoptera, which are oval and 

 very convex, and which swim poorly. They are yellow, spotted with 

 black. Their metasternum has an ante-coxal piece separated by a dis- 

 tinct suture, and their antennas are ten-jointed. 

 The CAEABID^E number probably over ten thousand described species, varying in 

 size from very minute forms up to beetles from two to three inches in length. Drs. 

 Le Conte and Horn give the following characters by which species of this family can 

 be readily distinguished from other adephagous coleoptera : Metasternum with an 

 ante-coxal piece, separated by a well-marked suture, reaching from one side to the 

 other, and extending in a triangular .process between the hind coxae ; eleven-jointed 

 antennae arising at the side of the head, between the base of the mandibles and the 

 eyes ; hind coxae mobile and simple ; and habits terrestrial. These beetles have 

 slender legs, and run rapidly ; the wings are often poorly developed. On account of 

 their rapid running habits, the Germans term these Coleoptera " Laufkafer." Sonorific 

 organs are not common in insects of this family, but species of Blethisa and of 

 JElaphrus stridulate. Luminous organs have been reported in the case of Physodera 

 noctiluca from Java. 



A large number of Carabidae have anal glands, which have been mistaken by some 

 writers for urinary organs, but which are defensive in function. The muscular bladder- 

 like receptacles of these glands are two in number, one on each side of the terminal 

 portion of the intestine, and each opens just above the rectal opening. Into these 

 receptacles, which serve to store the defensive fluid until needed, open the ducts of the 

 glands which prepare the secretion. In most cases the secretion is an odorous acid 

 liquid, which can be spurted out quite a distance, and Pelouze has shown that, in cer- 

 tain species of Carotins, this secretion contained butyric acid, the same acid that 

 imparts its indescribable odor to rancid butter. In Brachinus and a few 

 other genera the secretion of the anal glands is either partly gaseous on 

 emission, or becomes a permanent gas immediately afterwards, as can 

 be readily proved by compelling one of the insects to discharge its secre- 

 tion under water beneath an inverted test-tube filled with the same liquid. 

 In this way I have collected, in a few moments, from Aptinus displosor, FlG 47g _ Srachi _ 

 a Pyrenean species related to Brachinus, an amount of gas equal to sev- barc(ier*beetie )in 

 eral times the space occupied by the beetle itself. The discharge of the 

 anal glands of Brachinus, often rapidly repeated when the beetle is held between the 

 fingers, is accompanied by a smoke-like vapor and a popping sound, whence insects of 

 that genus are popularly termed bombardier-beetles. 



