INSECTA 483 



as the name of the order implies, a similarly short life. In the adult 

 the mouth parts are vestigial, no feeding is done, and the alimentary 

 canal, full of air, serves no longer for digestion. 



Economically these insects are of importance in so far as they con- 

 stitute a proportion of the food of freshwater fishes, the adults being 

 caught by fish during their nuptial dance, and the nymphs being de- 

 voured by bottom-feeding fish. 



Order MALLOPHAGA (Biting lice) 



These insects are ectoparasites of birds (less frequently of mammals). 

 Their reduced eyes, flattened form and tarsal claws are features corre- 

 lated with this mode of life. Unlike the Anoplura they have no 

 piercing mechanism and devour with biting mouth parts small 

 particles of feathers, hair, or other cuticular matter. 



The common hen louse, Menopon pallidum (Fig. 334), may be taken 

 as an example. The head is semicircular in form and articulates with 

 a prothorax which is freely movable on the rest of the body, a tagma 

 formed by the fusion of the meso- and metathorax with the abdomen. 

 The mouth is placed ventrally on the head and surrounded by biting 

 mandibles and less prominent ist and 2nd maxillae. 



Eggs are laid separately on feathers or hairs and the life cycle is 

 completed in about a month — the young instars resembling the adult 

 in form and habit. 



The various families of biting lice are strictly confined to particular 

 groups of birds, indicating that evolution of the parasites has pro- 

 ceeded concurrently with that of their bird hosts. 



Order ANOPLURA (Sucking lice) 



Ectoparasites of mammals, with mouth parts adapted for piercing the 

 skin and sucking the blood of their hosts. The eyes are ill-developed 

 or absent. The single-jointed tarsus carries a large curved claw ad- 

 mirably adapted for clinging to the host. The thoracic segments are 

 fused, and a flattened abdomen of nine segments possesses large 

 pleural areas allowing the body to swell on feeding. 



The minute mouth parts are accommodated at their bases in a 

 stylet sac which is a diverticulum ventral to the pharynx. There are 

 two stylets of which the dorsal is a paired structure, the halves of which 

 maintain contact with each other Idistally to form a half-tube which 

 is completed by the ventral stylet. This also consists of two elements. 

 Between the dorsal and ventral stylets lies the salivary duct which 

 appears to be a modification of the hypopharynx. The stylet complex 

 can be sufficiently everted so as to make contact with the skin. Into 



