656 MEDICAL ENTOMOLOGY 



it divides into two branches, both of which pass backwards and out- 

 wards, the upper one to end near leg IV, the lower to turn inwards and 

 backwards and to end at the posterior border. 



In Argas persicus the mid-intestine terminates in a round cul-de-sac 



which is in reality the first part of the hind-intestine. A short broad 



posterior or postero-lateral diverticulum (p. 1. d.) arises 



Posterior diverti ^ Qm gach ^ Q ^ t h e mid-intestine a little above its 



CUI8 



termination ; after a short course outwards each tube 

 passes backwards and divides into two main branches, each of which 

 splits into two secondary branches. The main external branch goes out- 

 wards and then backwards to the posterior border, where it turns 

 upwards to end on the ventral surface of the body ; the main internal 

 branch passes backwards, and at the posterior border turns upwards, 

 its branches ending in the vicinity of the rectum. The main branches, 

 together with their secondary branches, occupy the posterior third of the 

 body when full of blood. 



In O. savignyi the mid-intestine ends directly in four large posterior 

 diverticula (Plate LXXXIII, fig. 4), which arise close together from the 

 end of the intestine and are unbranched. They pass backwards to the 

 posterior border and then turn upwards to end near the rectum. 



In Margaropus there are two main posterior diverticula (Plate 

 LXXXIV, fig. 1), which arise from the sides of the mid-intestine ; after 

 a short course outwards they divide into two long branches, the external 

 of which runs outwards and then backwards, and turns upwards at the 

 posterior margin to end near the rectum ; the internal branch also goes 

 backwards parallel to the hind-intestine, and turns upwards on reaching 

 the posterior margin to end at the side of the mid-intestine. 



Much the same arrangement is seen in Hyalomma aegyptium (fig. 4) ; 

 the posterior diverticula, however, instead of arising each from a common 

 trunk, arise separately from the end of the mid-intestine as in O. savignyi. 

 They are very long, and the internal pair pass backwards below the ovary 

 on each side of the rectum to end near the anterior end of the mid- 

 intestine. 



In Ixodes ricinns, according to Samson, there are also four posterior 

 diverticula which arise separately from the mid-intestine. They pass 

 backwards parallel to each other and turn downwards and upwards on 

 reaching the posterior margin ; they end behind the ovary. 



From the above description it will be seen that the general arrange- 

 ment of the alimentary tract is very similar in the Argatini and Ixodini ; 

 in both there is an anterior and posterior set of diverticula with one or 



