122 FLEAS, FLUKES AND CUCKOOS 



speed and manner of their movements. Most species can run backwards 

 and forwards with equal facility; the short round forms (Plate XXI) 

 living on the head and neck do not move great distances, but can slip 

 speedily out of sight into the down at the base of the feather; the narrow 

 elongate forms found on the larger feathers of the body and wings, are 

 fast movers and able to slip sideways across the breadth of the feather 

 and from feather to feather with great rapidity. 



The legs are comparatively uniform throughout the bird lice. In 

 the Ischnocera they are adapted for clinging to the feathers by means of 

 the shortened tarsus and paired tarsal claws (Plate XXI). In the 

 Amblycera, which move more generally over the surface of the body 

 and feathers of their host, the legs have a longer tarsus, and are able, 

 through a modified part of this segment, to cling to smooth surfaces ; 

 thus they can climb up the sides of a glass tube, whereas the Ischnocera 

 cannot do so. 



The Mallophaga are photonegative and have a positive reaction to 

 the warmth and the smell of their hosts, reactions which ensure that the 

 lice keep well within the plumage, and do not stray off their hosts on to 

 other objects which may come within reach. On the death and corrup- 

 tion of the host, when the stimuli of temperature and smell undergo a 

 change, the lice come to the surface and can be seen moving restlessly 

 over the feathers. 



Their eyes are probably only able to perceive the difference between 

 light and darkness, and the movement of other objects. Each eye is 

 protected by a sensory hair (Plate XXI) which serves as a tactile 

 sense organ, probably helping to guide the louse in its passage through 

 the feathers. 



The antennae (Plate XXI), which can be seen in a constant state 

 of motion in the living louse, are also used as tactile organs in the 

 Ischnocera and in some of the Amblycera, but in this latter group they 

 may be small and completely enclosed in a fold of the head. They also 

 bear sense organs which are possibly connected with the perception of 

 warmth and smell similar to those in the antennae of the sucking louse 

 of man. The male antennae (in the Ischnocera) may be used to clasp 

 the females during copulation, and in some species (Plate XXIIIa) they 

 are larger than those of the female and have hook-like appendages 

 which improve their efficiency as clasping organs. 



All parts of the body bear numerous hairs or setae which are supplied 

 with nerve fibres, and serve as further tactile organs. 



