229 



NOTES ON PARASITIC ACARI. 



A. On the Presence of a System of Tracheal Tubes in the Families 



Sarcoptidae and Listrophoridae. 



B. Note on the Two Valid Species of the genus Psoroptes (P. 



natalensis and P. communis). 



By Stanley Hirst. 



{Published by Permission of the Trustees oj the British Museum.) 



(Read June 14th, 1921.) 



Figs. 1-3 in the Text. 



A. On the Presence op a System of Tracheal Tubes in 

 THE Families Sarcoptidae and Listrophoridae. 



The mites of the families Sarcoptidae and Listrophoridae are 

 considered by the great majority of authors to belong to the 

 order Astigmata, chiefly characterised by the absence of stigmata 

 and of tracheal tubes. It is true, however, that Megnin j&gures 

 a supposed stigmata in Chorioptes ecaudatus (see fig. 7, pi. xxi. 

 in Parasites et Maladies Parasitaires), and in a recent paper 

 {Bull. Soc. Zool. Paris, 1916, p. 61) Trouessart affirms his be- 

 lief in the presence of stigmata in Analgesidae and Sarcoptidae. 

 The presence of tracheal tubes in Acari of these families has not 

 yet been recorded, however. Whilst examining a preparation 

 of Otodectes cynotis var. cati kindly lent the author by Dr. J. H. 

 Ashworth, of the University of Edinburgh, it was noticed that 

 distinct tracheal tubes distended with air were clearly visible 

 in three of the mounted specimens, and it was possible also to 

 trace them in specimens of the variety furonis (from ferrets). 

 The distribution and general appearance of the system of tracheal 

 tubes in Otodectes is shown in fig. 1. It will be seen that 

 there is a tube on each side of the body, running posteriorly at 



