TWO SPECIES OF PARASITIC MITES. 339 
that of Sarcoptes scabiei, except that the wrinkles are much fewer 
and finer. At the anterior end of the body the organs of manducation 
are grouped together into the form of a sub-quadrate rostrum, which 
projects considerably beyond the front of the cephalo-thorax, though 
it is, to a certain extent, retractile under it. The rostrum, seen from 
the dorsal surface, is somewhat rectangular in outline, the outer 
angles being slightly rounded off and the line of the front curved 
outwards to a certain extent. Its length is considerably greater 
than its breadth, being on an average about 0.025 mm. broad and 
0.015 mm. long. It is composed essentially of the following parts, 
viz.: (1) A long delicate lingua, or tongue, which, however, is very 
difficult to discern clearly until the animal has been submitted to 
strong pressure, when it sometimes may be seen asa stout bristle 
projecting beyond the anterior margin. (2) A pair of long, acutely 
conical unjointed mandibles running parallel and close together during 
the greater part of their length, and apparently forming a sheath for 
the median tongue. (3) A pair of mazxille firmly united at their base, 
but bearing at their outer and anterior angles a pair of two jointed 
palps, one on each side of the mandible, the first joint being large 
and sub-rectangular, the second small and conical. Towards the 
side from the insertion of the palp, the angle of the maxilla is 
extended into a short spine. With the exception of the characters 
which we have just enumerated, namely, those of the skin and of 
the rostrum, and perhaps also those of te digestive canal, which 
however we have not been able to make out, the male and female 
present an entirely different appearance, and it will be most con- 
venient to consider them separately. 
In the male, which as stated above is flattened from above down- 
wards, the legs arise on the ventral surface a short distance in from 
the lateral margin, so that the first and part of the second joints are 
hidden from view when looked at from above. The number of 
joints present in each of the legs is four, the second probably corres- 
ponding to the second and third in Myobia musculi, and other closely 
allied species. They are all strengthened by very light brown rings 
of chitin which encircle them and form points of attachment for the 
flexor muscles. The first joint in all the eight legs is somewhat 
triangular in outline, the base of the triangle, which is the side 
nearest the middle line of the body, being somewhat incurved, with 
the angles adjacent to it slightly rounded, the anterior angle running 
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