116 
The Respiratory System of Mallo2)haga 
An examination of the literature concerning the occluding apparatus 
shows that the subject is still in a state of considerable confusion. 
Mjbberg (1910, p. 220) figures the occluding apparatus of Phthirus 
pubis (Anoplura) after Landois (1864). with a single extrinsic occlusor 
muscle; and gives original figures {l.c., p. 221) of the same apparatus 
in Haematopinus stiis (Anoplura) and Gyropus ovalis on the same plan. 
But Krancher (1881) had already figured Haematopinus suis with an 
intrinsic muscle only. Solowiow (1909), whose work I have only seen 
in summarised form, criticises the results of both Landois and Krancher; 
and finds, in lepidopterous forms, a third muscle present, the so-called 
musculus Versoni first indicated by Verson in Bombyx mori. This 
muscle I do not find in either Mallophaga or Anoplura. The remaining 
Fig. 19. Abdominal stigma of Heterodor.us longitarsus in optical section. 
two, the musculus constrictor and musculus tendinosus, have somewhat 
similar relations to those which I describe, but I refrain from actually 
homologising them. Landois and Thelen (1867) figure an orthopterous 
stigma with an intrinsic occlusor, and with a second muscle arising 
from the point at which this is inserted into the closing bow, the other 
insertion not being given. This structure does not in any way resemble 
the arrangement found in Mallophaga. Finally Mammen (1912), 
after a detailed description of the stigmata in Heteroptera and Homo- 
ptera, summarises insect stigmata into four groups, according as they 
possess one extrinsic, one intrinsic, two, or three muscles concerned in 
closing the trachea. The simple type of Mallophagan apparatus would 
fall into the second division of his first group, that in which a single 
