14 



STUDIES ON ACAKI. 



side, the palpi appear to form a single oval structure. Eacli palp can, 

 however, be protruded separately, and the second and third segments 

 are freely moveable. There is a well-marked tubercle or spine on this 

 segment which differs greatly in development in the different species 

 and affords a good specific character. It is very mmute m D. foUtcti- 

 lorinn (text-fig. 4 A) and in 1). phiilloides, and was thought to be an eye 

 by Erasmus Wilson, and also by Csokor. In D. canis the spine is quite 

 short, curved, fairly stout at the base, the end being narrowed and 

 pointed (lext-fig, 4 B). In the Demodex of tlie cat the spine is like 

 that of B. canis, but very minute (text-fig. 4 D). That of U. lonyior is 

 very similar to the one present in D. canis, being short and bent, but its 

 end is rather blunt. The spine is short and practically straight in 

 I), bovis, but sometimes there is the merest trace of an angle quite close 

 to the end ; sometimes there are two slight denticles at the end (text- 

 fig. 4 E & F). In D. equi it is slender and rod-like, only slightly 

 curved (or rather enlarged near the middle), the end blunt (text-fig. 4 C). 

 Tliat of U. rnnscardini is not very long, being curved, and fairly wide 



Text-fig. 4. 



Dorsal spine on capituluni (palp) of various species of Demodex. 



A. That of D. Jolliculorum. B. That of D. canis. C. That of D. equi. D. Tliat of I), caii. 

 H & P. Spine of B. lovis (showing variation in form). G. That of D. muscardini, 

 , H. That of Z>. ratti. I. That of D. arvicoJce var. musculi. 



at the base, but the greater part of the length of the spinels slender 

 and cylindrical, the end being rather blunt (text-fig. 4 G). The spine is 



