376 NATURAL HISTORY OF ARTHROPODS. 



is ahvnvs coveretl by the elytra, aiitl the beetles are usually somewhat elongate. 

 Althouiih the si)ecies belonging to this family are generally nearly monocolorous — 

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

 o-reater in number. Some of the species have stridtilating organs. The larvie of the 

 Lucanida* resemble closely those .of the SearabiTjidiv ; 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 maxillse, the antennse 

 are sjeniculate, the eyes emarginate, the anterior tibise toothed on the outer edge. X. 

 duma, from the eastern part of Xorth 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 L\icanus, are much enlarged, and have a single tooth on the inner side. 

 L. 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 L. cerims, the European stag-beetle, which latter is, however, somewhat larger. 

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

 tenna of four joints, and the anus in a longitudhial cleft. 



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

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

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

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

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

 is highly jiolished, the prothorax being smooth, the elytra 

 striate. Tliese beetles, with their M'hite 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 arc readily recognized by their very 

 poorly developed jiosterior legs. They further differ from 

 those of Liicamis in having a slenderer form, thi'ee-jointed 

 antennae, and the anus in a transversal cleft. The intestines 



Fig. 437. — Lucanus dama. ' . . -r« r 



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

 Joseph Leidy has described protophyta, protozoa, and nematode ^\'orms from this 

 insect. 



The Parxid.e include a small number of beetles which are united in one family 

 more by their resemblance as larva? 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 adheij^-s to this pubescence when the beetles are beneath the surface of 

 water, for they are all aquatic in habits. 



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

 and most of tliem 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 are attached filamentous 

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

 segment,?, and have no relation to the stigmata. The internal trachea3 are moulted 

 througli the closed stigmata. One species which lives in moist air lias eight pair: 



