ON DEMODEX PHYLLOIDES. 277 



Demodex may be conveyed from dog to dog, yet experimental 

 attempts to prove this have failed, and very often one dog in a 

 kennel may be affected, and, although mingling freely with the 

 others, may be powerless to infect these. 



2. — Systematic Position. 

 After discussing the results of previous observers as to the 

 anatomy of Demodex, he concludes under his second heading that 

 five well marked varieties may be distinguished, all referable to that 



genus, viz. : 



D. folliculorum hominis. 

 D. folliculorum canis. 

 D. folliculorum cati. 

 D. phyllostomatis {Leydig). 

 D. phylloides (C'sokor). 



The genus he regards with Koch as forming an independent 

 Family of the Acarina the Dermatophili. 



3. — Natural History of D. Phylloides. 



The form of the body and its division into three regions, head, 

 thorax and abdomen (the last distinguished by the absence of 

 appendages and of the chitinous framework present in the thorax), 

 may be studied in Figs. 7 and 8. 



The result of a series of comparative measurements shows : 



1. That D. phylloides (length, male 0.22 mm., female 0.24—0.26 mm. ) 



reaches the minimum length of D. canis, but never that of D. 

 hominis. 



2. Head and thorax are together equal in length to the abdomen, 



while in D. canis they only form a third of the whole length of 

 the body, and in D. hominis only a fourth. 



3. D. phylloides is comparatively almost twice as broad as D. canis 



or hominis. 



4. The head in D. phylloides is absolutely both longer and broader 



than that of either D. canis or hominis, a circumstance which 

 renders the analysis of the appendages of the head easier in this 

 species. 



5. The egg is more oval than spindle-shaped, and both it and the 



larval stages are longer and broader than the similar stages in 

 D. canis and hominis. 



6. There is more difference between D. phylloides on the one hand, 



and D. canis and hominis on the other, than there is between 

 these two last-mentioaed varieties. 



