232 Mr. S. Hirst on certain Species of 



XXIV. — Remarks on certain Species of the Genus DemoJex, 

 Owen (the Demodex of Man, the Horse, Dog, Rat, and 

 Mouse). By Stanley Hirst. 



(Publislied by permission of tlie Trustees of the British Museum.) 

 [Plate IX.] 



Demodex foUiculorum, Simon. 



Elongated specimens of Demodex foUiculorum (from human 

 beings) are from five and a half to over six and a half times 

 as long as tiie width of the cephalothorax *, the latter (in- 

 cluding capituhiin) being about a quarter of tiie total length 

 in large specimens. Capitulum siiort, being much wider 

 than long ; the two spines on its dorsal surface are very 

 short and inconspicuous. 



This species is apparently the longest of the genus, adult 

 females sometimes measuring up to 390 jx in length. 



Demodex caninus, Talk. 



D. caninus is an elongated species, being usually more 

 than six (sometimes up to seven) times as long as wide. Tlie 

 cephalothorax (not including capitulum) is a little less than 

 half the length of the abdominal part of the body and is of 

 moderate width. Abdomen long and slender, gradually 

 tapering to the posterior end, which is bluntly pointed. 

 Capitulum of moderate width, being widest at the base, 

 where it about equals its length ; the two spines on its dorsal 

 surface are very short and pointed. 



Measurements. — Length of body 225 fi ; width of cephalo- 

 thorax 40 /i. 



Material. — Numerous specimens from a dog suflfering from 

 the disease induced by this species of Demodex. 



Note. — My adult females of D. caninus do not measure 

 more than 225 fx, whereas Canestrini states that his examples 

 of this sex measure up to 302 /jl ; from this it would seem 

 that this species varies considerabl}^ in length when adult. 



* The word " cephalothorax " is used here to indicate the anterior 

 part of the body bearing all the four pairs of le<rs. It is, perhaps, neces- 

 sary to make "this point clear, for the last pair of legs in the genus 

 Demodex sometimes has the appearance of being placed on the " abdo- 

 men " ; this is due to the fact that the transverse striations (or annulatious) 

 characteristic of the posterior region of the body extend dorsally beyond 

 this pair of legs (or even further forwards in some species). 



