234 On certain Species of the Genus Demodex, Owen. 
pointed. Spines on dorsal surface of capitulum quite long 
and pointed at the end. Cephalothorax fairly wide. There 
is an internal chitinous structure in one of the specimens 
which seems to be a penis; it is shaped as figured (text- 
fig. 2a). 
Besides a few adult specimens, I have been able to mount 
and examine two examples of a much more elongated form, 
which is apparently a nymph (although very much larger 
than any adults of this species so far collected, no traces of 
the genital opening can be detected). The body (including 
capitulum) of this nymphal form is about seven and a half 
times as long as the width of the cephalothorax. Its abdo- 
men is rather more than two and a half times the length of 
Fig. 2. 
Demodex musculi, Oudms. a, penis; 6, dorsal view of capitulum. 
the cephalothorax+the capitulum. Pl. IX. fig. 2, gives a 
good idea of the appearance of this elongated form, but the 
length is shown a little too short. The legs are rudimentary 
in this nymph, and their structure is difficult to ascertain 
with certainty; there are also four pairs of small rounded 
structures near the middle line, which are, perhaps, the basal 
segments of the developing legs of the adult. 
Measurements.— 2. Length of body (including capitulum) 
150 »; width of cephalothorax 22-38 w. Length of body 
of g 125, of large nymphal form 235 «4; width of cephalo- 
thorax 30 pw. 
Material—Four tame mice were examined, and the Demo- 
dex was discovered in three of them, but the parasites were 
very few in number. 
