232 Mr. S. Hirst on certain Species of 
XXIV.—Remarks on certain Species of the Genus Demodex, 
Owen (the Demodex of Man, the Horse, Dog, Rat, and 
Mouse). By STANLEY Hirst. 
(Published by permission of the Trustees of the British Museum.) 
[Plate IX.] 
Demodex folliculorum, Simon. 
Elongated specimens of Demodex folliculorum (from human 
beings) are from five and a half to over six and a half times 
as long as the width of the cephalothorax *, the latter (in- 
cluding capitulum) being about a quarter of the total length 
in large specimens. Capitulum short, 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 w in length. 
Demodex caninus, Tulk. 
D. caninus is an elongated species, being usually more 
than six (sometimes up to seven) times as longaswide. The 
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 » ; width of cephalo- 
thorax 40 pw. 
Material_—Numerous specimens from a dog suffering from 
the disease induced by this species of Demodea. 
Note.——My adult females of D. caninus do not measure 
more than 225 w, whereas Canestrini states that his examples 
of this sex measure up to 302 w; from this it would seem 
that this species varies considerably in length when adult. 
* The word “cephalothorax” is used here to indicate the anterior 
part of the body bearing all the four pairs.of legs. 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 annulations) 
characteristic of the posterior region of the body extend dorsally beyond 
this pair of legs (or even further forwards in some species). 
