65 : 4 MEDICAL ENTOMOLOGY 



it is a narrow tube of a whitish colour, but in some species it may contain 

 digested blood. It passes down to the posterior surface of the rectum ; 

 the two long Malpighian tubes enter the rectum on either side of it. 

 The rectum will be recognized as a large grey or black sac lying about 

 the middle of the ventral surface and at the junction of the middle and 

 posterior parts of the body; it often has accessory diverticula, as in 

 Argas, to be described presently. 



The testis and ovary lie slung across the body above the posterior 

 diverticula and rectum ; the ovary is readily recognized by the pre- 

 sence of the ova. 



The alimentary canal consists of a central tube with a number 



of secondary branches or diverticula, which are blind sacs capable 



of great distension. The central tube is short and 



The Alimentary lies in the middle of the body ; it extends in an 



intestine ancMts antero 'P oste " or direction and is here referred to as 

 diverticula. Plates tne mid-intestine. When the mid-intestine and its 

 LXXXIII and LXXXIV diverticula are full of blood they form distinct pro- 

 minences on the dorsal surface of the tick. 



The anterior end of the mid-intestine may divide into two sets of 

 diverticula, an antero-lateral and a lateral set ; in addition to some species 

 (Ornithodorus) there is an antero-median branch. In Argas persicus 

 (Plate LXXXIII, fig. 1) the antero-lateral diverticulum (a. 1. d.) passes 

 forwards and outwards and divides into three branches. The anterior 

 branch (a. b.) passes directly forwards and divides into three short 

 branches ; the external of these ends opposite coxa I, the middle, 

 often the longest, bends inwards near its extremity and ends near 

 the pharynx ; the internal branch also ends in the same situation. 

 These secondary branches are very constant in their arrangement. 



The middle branch (m. b.) of the antero-lateral diverticulum passes 

 outwards and soon divides into three short finger-like processes. The 

 posterior branch (p. b.) is much longer and passes backwards and out- 

 wards towards leg IV ; it then bends inwards and divides into two short 

 branches. 



In Ornithodorus savignyi and O. moubata the mid-intestine also 

 gives off an antero-lateral branch (fig. 4, a. 1. d.), which after a short 

 outward course sub-divides into an anterior and a posterior branch. The 

 anterior branch (a. b.) passes forwards and divides into three secondary 

 branches as in Argas persicus. The posterior branch (p. b.) extends out- 

 wards and divides into two long branches, both of which pass downwards 

 and inwards to end behind the salivary gland ; it is not uncommon to 



