EXTERNAL ANATOMY 683 



to be of a sexual nature : the appendage is shorter and broader than 

 that of the female, and in place of the external digit there is a long 

 blade-like slip of chitin with a delicate hooked hair on its inner side ; 

 in place of the internal digit there are two rod-like pieces of chitin, one 

 of which is hooked at its end like a shepherd's crook. Attached to the 

 ventral side of the end of the mandible there is a club-shaped pad, 

 directed inwards towards its fellow of the opposite side, and with a 

 fringe of delicate hairs along its margin. 



The maxillae are situated at each side of the buccal cavity, above the 

 lateral arms of the hypostome, and are much smaller than the mandibles. 

 Each is a flat and narrow blade of chitin, ending in a sharp point and 

 evidently intended for piercing. The hypostome is situated on the 

 ventral side, and is spatulate and divided into a central cone-shaped 

 portion and two lateral arms, which lie just below the maxillae. The 

 hypostome is not armed with recurved fixing teeth, and therefore probably 

 does not fulfil the same function as in the ticks. As all blood-sucking 

 gamasids are intermittent feeders the hypostome, like that of the 

 Argatini, is only used as a cutting weapon. 



The food canal is formed by the apposition of the hypostome and 

 mandibles above and the maxillae below, the sides being closed in by 

 loose folds of the lateral integument. 



The palps are filiform, and consist of five short segments, the terminal 

 one of which is armed at its apex with a number of sensory hairs, grouped 



together as in the ticks. On the inner side of the fourth 



..... . The palps 



segment and just below its apex there is a large curved 



spine, shorter and stouter in the male than in the female; and in the same 

 situation in both sexes there is a pair of peculiar short spines with globular 

 ends. The second segment has a long spine on its internal border. 



The cephalothorax is covered dorsally by the scutum, which in the 

 female almost completely conceals it ; the scutum is seldom marked with 

 spots and colour designs. The stigmata are situated 



in the usual position behind and external to coxa IV ; 8tructure of bod : 

 , . 11 j i j j j c A scutum, stigmata 



the pentreme is well developed and extends forwards and p | ateg 



to the dorsal surface. The ventral surface is provided 

 with shields very much as in the ticks ; there is a sternal plate as well as 

 genital and anal plates ; in some mites in addition there are one or 

 more small accessory plates. The female genital opening is situated 

 between the sternal and genital plates, the male opening on or near 

 the sternal plate. The anal opening lies on the anal plate and often has 

 a large spine on its posterior margin. 



