INSECTA 185 



and maxillae. The former are slight structures of unequal length 

 which taper towards their free end, where they are edged with a 

 row of fine teeth. The maxillae are broader, but they also taper 

 towards the free end ; they are of equal length, and are furnished 

 with a small disc-like appendage, placed just in front of the pointed 

 tip. In shape the maxillae resemble two gutters, the concave 

 surfaces of which face one another and so form a tube. This tube 

 serves to conduct the blood from the wound into the pharynx, and 

 also to convey saliva into the wound. 1 To the sides of and beneath 

 these tubes lie the two mandibles ; these are opened during the act 

 of sucking by the agency of several groups of muscles, which proceed 

 from the inner surface of the cuticle of the head and are attached 

 to the dorsal wall of the pharynx. The action of these muscles is 

 counteracted by the elasticity of the cuticle of the pharynx, while 

 the saliva is expelled by means 

 of a syringe of complicated 

 structure, situated ventrally to 

 the pharynx, and with which 

 the ducts leading from the 

 salivary glands communicate. 



(2) Lice. Lice live upon 

 the epidermis of warm-blooded 

 animals. They are divided into 

 two groups : Anoploura or 

 Khynchota aptera, true lice ; 



and Mallophaga, lice which 



. , . ^ ,. & ' FIG. 96.Phlhlriuspubis. 30:1. (After 



inhabit the appendages of the Leuckart.) 

 skin. The latter are furnished 



with biting mouth-parts and draw their nourishment from horny 

 epidermis cells, hairs and feathers. Of this group the only species 

 of interest is Trichodectes, which harbours the Cysticercus of Dipy- 

 lidium caninum, L. True lice are found only upon mammals, whose 

 blood they suck. They are provided with sucking mouth-parts, which 

 are prolonged backwards into the head, but are protruded when in 

 use. Two genera occur on man (Pediculus and Phthirius) and one is 

 found on the domestic mammals (Hcematopinus). 2 



Phthirius is distinguished from Pediculus and Hcematopinus, which 



1 In other Hemiptera, food and saliva are conveyed by two distinct channels, 

 formed by a longitudinal ridge which runs down the groove of each maxilla, dividing 

 it into two parts. Thus, when the maxillae are closed two parallel tubes are formed, 

 of which the upper leads to the intestine, while the lower one is in communication 

 with the salivary glands. 



2 This family has recently been divided into several groups by Enderlein (Zool. 

 Anz., vol. xxviii, 1905). 



