L. Harrison 
100 
segments three to seven carry the spiracles; but in the latter, though 
the first pair is reckoned as occurring on the third segment, the first 
segment is so much incorporated with the thorax that only a small portion 
of the tergum, which does not reach to the sides of the abdomen, remains. 
In the Boopidae there is also a suggestion of the inclusion of an abdominal 
segment with the thorax, as a sternite quite distinct from that of the 
metathorax is visible on the under side, for w'hich there is no corre¬ 
sponding tergum on the dorsal surface. It is reasonable to conclude 
that the same cause operates in the case of both Kicinidae and the 
IscHNOCERA, and that the difference in stigmata! arrangement is due 
to the suppression of the first abdominal segment, or its incorporation 
with the thorax. This condition is strongly suggested in Trichodectes. 
The segments in front of those which bear the stigmata usually show 
Fig. 9. Philo'pterus brevicollis; (A) Part of first three abdominal segments to show 
stigmata and stigmatal scar; (B) sixth abdominal stigma in profile. 
small scars in the position which the spiracles would have had (Fig. 9), 
and indicate that the Mallophaga, or their ancestors, originally had two 
additional pairs of abdominal stigmata. 
The abdominal stigmata open indifferently through terga, or pleut’a, 
or the softer integument separating the two. They are almost invariabl}^ 
dorsal, and usually perforate the terga in the Ischnocera ; but in the 
Amblycera the more posterior tend to become lateral, or even ventral. 
In Gliricola all are ventral, piercing the pleura. In many species, 
more especially of Ischnocera, each is surrounded by a clear pustide 
(Fig. 9). In others, as, for example, Goniodes and Trinoton, heavy 
pleural or tergal incrassations surroifnd the stigmata. They are all 
alike in form, an external circular or ellipsoidal opening leading into a 
