18 



STUDIES ON ACAET. 



differ in closely allied species. The position of the male genital orifice 

 is also somewhat different in some of the species. The structure of the 

 ova and immature stages should also be studied, as they serve to help 

 to distinguish allied forms from one another. Even the adults of 

 Demodex vary very greatly in size (especially D. folliculoruni and 

 I), canis), and it is a great mistake to rely upon measurements alone 

 when comparing species of this genus. Some of the early workers 

 obviously have only measured the largest specimens they met with, 

 and it is probable that the sex of some of their specimens is wrongly 

 given. 



With the exception of D. hovis from the Belgian Congo, and 

 B. phylloides from the Argentine, all the forms of Bemodex dealt with 

 below are described from examples from English hosts. The measure- 

 ments were made with a Zeiss Stufen (step) ocular micrometer, the 

 values of the scale being obtained in the usual way by combination 

 with a stage micrometer. The figures have been carefully drawn by 

 Mr. Percy Highley with the aid of an Abbe camera lucida. 



LIST OF THE SPECIES AND VARIETIES OF THE GENUS DEMODEX 

 WITH THEIK HOSTS AND KNOWN DISTKIBUTION. 



1 . Demodex folliculorum Simon 



2. D. amis Leydig . . . 

 D. cams var. ovis Eailliet 



D. canis var. erinacei Hirst , 



3. D. longtor Hirst ... 



4. D. cati Mcgnin 



5. D, 'phijlloidet Csokor . . 



6. D. bovis Stiles Cattle {Bos taurus). 



7. D. equi Bailliet 



(recorded from Sweden , 

 Germany, France, Spain, 

 Algi'ria, Madagascar, 

 Canada, the United States, 

 Argentine, and New 

 Zealand). 



Probably Cosmopolitan 

 (Scandinavia, Germany 

 Italy, North and South 

 America, Tropical Africa, 

 Miidiigascar). 



Horse {Equus cahallut). Probably Cosmopolitan 



(Scotland, England, France, 

 Germany, Brazil). 



