ON DOTS (LARVAL (ESTRID^b) OF THE HORSE AND CAMEL. 



29 



Hooklcss or orifice end. — Opening ob- 

 long. Its cavity black throughout. 

 Its lips transversely bifid and the lower 

 one much larger than the upper. 

 The upper one continuous laterally 

 with the side lobes. The last 

 segments are arranged telescopically 

 and bear no appreciable spinelets. 



sense organs (situated above the booklets above and below. This first 



books). These sense organs are zone is a very irregular one. There 



all but sessile. The first row of is no chitinous organ between the 



spines is complete. hooks. The pigmented sense organs 



are on long peduncles the bases of 

 which are connected by a baud. 

 There is another transverse band 

 below the hooks. The first row of 

 spines is deficient inferiorly. 



Hookless or orifice end.— Opening an 

 almost circular cavity, black only in 

 two lateral spots, upper lip semi- 

 circular and with four well marked 

 angles, lower bifid, consisting of a 

 tuberous part elongated transversely 

 and also of two bifid protuberances 

 each bearing a mammillary process. 

 There are spinelets on the two latter 

 and on the lower lip. The general 

 aspect of the opening is upward. Last 

 segment irregularly telescopic. 



The characters amply prove that the camel bot serves as a 

 connecting link between the peculiar tough horse bot and ordinary 

 maggots, they show that the strange leathery spines of the horse 

 bot are not chitinous or horny nails but true papilke, they show 

 that these papilla? tend to arrange themselves in groups and some 

 develope into foot-like organs while the others lose their importance. 

 By contrast of these organisms with common maggots we may infer 

 what features of structure are necessary for a grub that lives in the 

 stomach (as the horse bot does) and what for a resident in the 

 pharynx (as the camel bot). The latter it will be noticed is softer 

 and less irritant than the former and probably, as having rudimen- 

 tary false legs, a much better traveller. He makes his exit from 

 the body through the nose, whereas the stomach bot of the horse 

 passes through the anus. The difference in position of the hooks 

 is interesting ; the camel parasite has them arranged like a pair Of 

 delicate anchors, which he can throw down when he wishes to obtain 

 a grip sufficing to prevent his being swallowed with food, whereas the 

 horse parasite has much stronger grappling hooks arranged like the 

 hums of a stag beetle and suited to enable him to hold tight in 

 whatever direction the churning motion of the stomach may drag 

 him. 



