32 BULLETIN 67, UNITED STATES NATIONAL MUSEUM. 



SIFHOXAI'TERA. 



This order, comprising a single family, Pulicidae, or fleas (fig. 64), 

 is not a large one in point of species, but nevertheless manages to 

 attract the attention of mankind. The fleas never have wings, but 

 nature, always compensating, has endowed them with most remarkable 

 leaping ability. The body is compressed, and the segments fur- 

 nished with rows of bristles, and often some stiff spines. These spines 

 are usually set upon the lower margin of the head and the posterior 

 border of the pronotum, and each series is known as a comb or ctenid- 

 ium. The antennae are very short and lie in a groove near the small 

 eyes. The mouth-parts are slender and suited for piercing the skin 

 of the host and sucking up blood. The legs are very bristly, but not 

 very large, and apparently incapable of producing the amazing leap. 

 The larva of a flea is a slender, legless creature occurring under car- 

 pets, in cracks, near the nests of animals, etc., and feeds on refuse, 



dirt, and bits of decaying vegetable 

 matter. When full grown they spin 

 a cocoon within which they transform 

 to the pupa, and later issue as adult 

 fleas. In the past few years one of 

 the rat fleas, Xenopsylla cheojris, has 

 been connected with the dissemina- 

 tion of bubonic plague. Fleas may 

 be taken from the host animals and 

 in these animals' nests. All should 

 be collected in vials of alcohol, and 

 mounted in balsam on slides for study. 



HYMENOPTERA. 



This order embraces a great number of insects, many of which are 

 known under the names of bees, wasps, and ants. They have four 

 membranous wings of moderate size, with but few cross veins, and 

 biting mouth-parts. In some cases the mouth is also fitted for sucking 

 or lapping up liquids, but the mandibles are still suited for biting. 

 The body is very compactly put together, and the skin is often very 

 hard, and in many cases the abdomen terminates in an ovipositor or 

 sting. The thorax of most Hymenoptera comprises not only the 

 three parts found in other insects, but also the first abdominal 

 segment. The transformations are complete. The larvae are usually 

 footless, but those of the sawflies have six true legs and often prolegs 

 which are more numerous than in lepidopterous insects. The Hyme- 

 noptera may be divided into suborders as follows : 



The Chalastogastra , or sawflies (fig. 65), in which the abdomen is 

 not constricted at base to form a petiole, and the first segment is not 

 united to the thorax. The trochanter of the legs (the small joint 

 between coxa and femur) is of two parts or joints. The tip of the 



