L. Harrison 
121 
There are seven pairs of stigmata, one thoracic, and six abdominal. 
Here again the reduction of the anterior segments of the abdomen is 
very marked. Two very short first segments each have well-marked 
stigmatic branches, but no stigmata, the latter lying, as in both the 
previous groups, typically in segments 3-8. The general arrangement 
of the main tracheal trunks, stigmatic branches and dorsal and ventral 
supply is on a similar plan to that of the Mallophaga; though the stig¬ 
matic branches usually form a plexus of two or three vessels with 
numerous anastomoses, in place of a single branch, and there are other 
differences in detail. 
This brief statement is enough to justify the conclusion that the 
respiratory system in Mallophaga, Anoplura, and Copeognatha, exhibits 
a remarkable correspondence. In all three groups there are one pair 
of thoracic and six pairs of abdominal stigmata, the latter typically on 
segments 3-8. In all three gi’oups there is evidence, in the shape of 
vestigial stigmatic branches, of the existence in past time of two 
additional pairs of abdominal stigmata; and in all three groups there 
is evidence pointing to the total or partial suppression of one or two of 
the anterior abdominal segments. 
The comparative literature on the number and position of insect 
stigmata is not sufficiently definite to allow of any positive statement 
as to affinity indicated by this common possession of the three groups 
mentioned above. But I consider the relationship of Mallophaga and 
Anoplura to be definitely established; and as the latter are still usually 
included among the Hemiptera on account of their sucking mouth- 
parts, and as we have a definite pronouncement on the number and 
position of the stigmata in this order, it may be useful to emphasise 
the essential difference between Hemiptera and Anoplura in this regard. 
Handlirsch (1899) gives the stigmata in Hemiptera as ten pairs, two 
thoracic on the two posterior segments, and eight abdominal on the 
first eight segments. He expressly points out that the Anoplura do 
not conform to this type. In his own words: “ Nur die durche ihre 
eminent parasitische Lebensweise stark modifizierte, vollkommen fiii- ' 
gellose Gruppe der Pediculiden (excl. Mallophaga) weicht starker von 
dem Grundtypus ab indem bei ihr ausser den zwei ersten abdominalen 
Stigmenpaaren auch jenes des Meta thorax verschwunden ist.” As no 
reason is advanced to connect specialisation following on a parasitic 
mode of life with an alteration in the number and position of the stigmata 
which, though it may possess morphological significance, can make 
little practical difference to the respiration of the group, it seems 
8—5 
