THE MID-INTESTINE AND DIVERTICULA 655 



find one of the posterior branches arising almost directly from the mid- 

 intestine (Plate LXXXIII, fig. 4, left side). 



In O. savignyi and O. moubata, in addition to the antero-lateral 

 diverticulum, there is a true lateral sac. (fig. 4 1. d.) This is a long tube 

 which passes outwards towards the point of origin of the tracheae from the 

 spiracles, where it divides into two branches. One of these, usually the 

 shorter, passes inwards towards the mid-intestine, then turns upwards 

 behind it and ends near the brain. The larger branch passes directly 

 backwards and ends near its fellow of the opposite side behind the posterior 

 diverticula. In O. savignyi and O. moubata there is also a short antero- 

 median diverticulum (Plate LXXXIII, fig. 4, a. m. d.) ; it extends straight 

 forwards to lie over the mandibles and ends near Gene's organ (g. o.), to 

 be described presently. This branch is not represented in any of the 

 other ticks examined. 



In Margaropus annulatns the antero-lateral diverticulum (Plate 

 LXXXIV, fig. 1) extends for a short distance directly outwards and 

 then divides into three branches. The first or anterior branch (a. b.) is 

 short and passes forwards to end, with its fellow of the opposite side, near 

 the pharynx. The second or median branch (m. b.) extends outwards and 

 a little upwards, and turns inwards and backwards at the level of leg II to 

 end under the salivary gland ; as a rule it is a long branch. The third 

 or posterior branch (p. b.) passes downwards and backwards and soon 

 gives off a lateral branch, which turns upwards and ends near the second 

 branch of the antero-lateral diverticulum. About the level of leg III the 

 posterior branch ends by dividing into two secondary branches ; the 

 external of these passes downwards and backwards to the posterior 

 border, where it turns upwards to end near the salivary duct. The 

 internal branch turns in towards the mid-intestine, then bends upwards, 

 and ends near the origin of the oesophagus from the mid-intestine. 

 In M. annulatns, as in O. savignyi, the two sides are often not symmet- 

 rical ; for instance, the third main branch of the antero-lateral diverticu- 

 lum on one side may extend for some distance before it gives off any 

 branch, and on the opposite side it may divide up almost immediately 

 after its origin from the main trunk. 



. In Hyalomma aegyptium (Plate LXXXIV, fig. 4) the antero-lateral 

 diverticulum (a. 1. d.) is arranged on much the same plan as that in 

 M. annulatns ; in this case, however, the third branch extends for a 

 considerable distance before it divides into its secondary branches. 



;. According to Samson, who has studied the internal anatomy of Ixodes 

 ricinus, the antero-lateral diverticulum in this species. is much simpler; 



