376 NATURAL HISTORY OF ARTHROPODS. 



is always covered by the elytra, and the beetles are usually somewhat elongate. 

 Although the species belonging to this family are generally nearly monocolorous — 

 usually shades of brown in temperate regions — in tropical species the colors are often 

 greater in number. Some of the species have stridulating organs. The larvsB of the 

 Lucanidse resemble closely those of the Scarabseidae ; they live in decaying wood, on 

 the juices of which the imagos also feed. 



In Lucanus the mentum is entire, and covers the ligula and maxillae, the antennae 

 are geniculate, the eyes emarginate, the anterior tibiae toothed on the outer edge. L. 

 dama, from the eastern part of North America, varies from 0.9 to 1.5 inches in length. 

 It is of a dark chestnut-brown in color, and the mandibles of the male, as is usual in 

 species of Ziucanus, are much enlarged, and have a single tooth on the inner side. 

 X. elaphus, whose mandibles are branched in the male, and often 0.75 of an inch long, 

 is called, on account of its antler-like mandibles, the stag-beetle. It closely resem- 

 bles X. cervus, the European stag-beetle, which latter is, however, somewhat larger. 

 The larvae of Lucamis , which inhabit dead wood, have six well-developed legs, an- 

 tennae of four joints, and the anus ip a longitudinal cleft. 



Differing from Lucanus, in having an emarginate mentum, are the species of Pas- 

 salus, which are numerous in some tropical regions, but of 

 which only one is found in the United States. This species, 

 P. cornutus, is flattened, cylindrical in form, about 1.25 

 inches long, and of a very dark-brown color. Its surface 

 is highly polished, the prothorax being smooth, the elytra 

 striate. These beetles, with their white larvae, are often 

 found in great numbers in half-decayed logs, and when taken 

 between the fingers emit a peculiarly delicate squeaking 

 sound. Their larvae are readily recognized by their very 

 poorly developed posterior legs. They further differ from 

 those of Lucanus in having a slenderer form, three-jointed 

 Fig 43T —Lucanus dama. antennae, and the aims in a transversal cleft. The intestines 

 of P. cornutus furnish a rich field for the microscopist. Prof. 

 Joseph Leidy has described protophyta, protozoa, and nematode worms from this 

 insect. 



The Paenid^ include a small number of beetles which are united in one family 

 more by their resemblance as larvae than by the structure of their imagos. The 

 beetles have in common the following characters : the dorsal segments of the abdomen 

 are partly membranous, the first to the third ventral segments are connate, the last 

 joint of the tarsi is long and the claws large. The body is very finely pubescent, and 

 a film of air adheres to this j^nbescence when the beetles are beneath the surface of 

 water, for they are all aquatic in habits. 



The larvae of the Parnidae are, according to Friedenreich, flattened oval in form, 

 and most of them adhere to stones under water by using their entire ventral surface as 

 a sucker. They consist of twelve segments, of which the first one later forms the 

 head and prothorax of the imago. The aquatic species have closed stigmata, and 

 respire by gills, from which air is distributed through a closed tracheal system. The 

 gills are tubular, and consist of a motile trunk, to which ai-e attached filamentous 

 branches. These gills are beneath the fourth to the ninth or the fifth to the tenth 

 segments, and have no relation to the stigmata. The internal tracheae are moulted 

 through the closed stigmata. One species which lives in moist air has eight pairs 



