668 LAURA FLORENCE 
numerous. Owing to the thickness of the cuticula it is impossible to 
watch the pulsations of the heart in living specimens, as was done by 
Landois (1864:11) and by Miiller (1915:29) in the clothes louse. 
The most successful preparations of the dorsal vessel have been obtained 
by first removing the dorsal cuticula of the whole abdomen and then the 
dorsal muscle plate. If the posterior attachment of the muscles of segment 
9 be carefully loosened, the heart and its wing muscles will generally be 
found intact on the ventral surface of the muscle plate. 
THE NERVOUS SYSTEM 
Since the time of Swammerdam (1682, English trans. 1758:36), it has 
been known that lice possess three large thoracic ganglia and no abdominal 
ganglia, and that nerves pass backward from the metathoracic ganglion 
over the ventral stomach wall. It was not, however, until almost two 
hundred years later that a more detailed description of the central nervous 
system appeared, when Landois (1864:24) published his description of 
Phthirius inguinalis. He referred to Swammerdam as correctly describing 
three thoracic ganglia, and to Burmeister (1847) as incorrectly describing 
two in the Pediculidae. He figured the brain, the connectives, and the 
thoracic ganglia, but showed neither a sub-esophageal ganglion nor a 
sympathetic system. In his study of Pediculus vestimenti, published a 
year later (Landois, 1865 a:54), he found no noteworthy difference between 
the species. Briihl (1871:477) devoted his attention chiefly to the study 
of the peripheral ganglia, which he described as “ Haar-Gehirne” and 
of which he counted approximately one hundred and fifty on each louse. 
Graber (1872:165) reviewed the work of Landois, and described the 
connectives between the brain and the thoracic ganglia as being ‘at least 
four times the length given by Landois. On one occasion he found and 
figured a pear-shaped ganglion with two nerves passing backward from 
it. He thought it was the hitherto undescribed sub-esophageal ganglion, 
but, since it lay on the dorsal surface of the esophagus, he concluded that 
it must be a part of the visceral nervous system. Myéberg (1910:222) 
did no work on the nervous system, but in a short note he mentioned the 
concentration of the ganglia in the thoracic region and the lack of any 
detailed work in both Siphunculata (Anoplura) and Mallophaga. A 
considerable advance has been made by Miller (1915:32-37) in his 
