670 LAURA FLORENCE 
ganglia. They measure approximately 0.22 millimeter in length. The 
thoracic ganglia are large and broad. Their approximate length is 0.38 
millimeter and width 0.28 millimeter. They are closely fused, showing 
neither connectives nor commissures, but both in gross specimens and 
in sections it is evident that each ganglion has arisen through lateral 
fusion of two ganglia. They lie in the most anterior part of the thorax, 
and when the stomach is distended their position is oblique dorso-ventral 
rather than ventral. All three send out lateral nerves to the legs and the 
thorax, and the metathoracic ganglion sends in addition eight nerves 
to the abdomen, of which the two nearest the median line are the largest. 
These nerves pass backward to the ninth abdominal segment and give 
off in their course many slender branches to the visceral and reproductive 
organs. 
The sympathetic system is well developed. The frontal ganglion is 
somewhat pear-shaped and lies some 0.03 millimeter in front of the brain, 
on the median line above the junction of the pumping pharynx with the 
true pharynx. Slightly laterad on either side of the ganglion a small 
nerve is given off anteriorly from the branches connecting the ganglion 
with the brain. The course of these nerves has not been seen, but they 
may connect the frontal ganglion with two smaller ganglia which are 
united to each other and lie on the median line above the anterior part of — 
the buccal plate of Harrison (Plate LX, 1). Similar ganglia have been 
seen by Sikora (1916:28) in the clothes louse, and she has suggested that 
they are homologues of the prefrontal nerve plexus described in other 
insects. From the anterior end of the frontal ganglion a nerve passes 
forward on the median line, and from it numerous lateral branches are 
given off. From the posterior end of the frontal ganglion the recurrent 
nerve runs back, passing under the brain close to the dorsal surface of the 
esophagus and finally terminating in the thorax. in a small ganglion 
situated above the entrance of the esophagus into the stomach. From 
this ganglion at least two slender nerves pass backward over the dorsal 
stomach wall. 
Both in gross dissections and in the study of serial sections, two sub- 
circular structures, of a diameter approximating 0.03 millimeter, have 
been found under the protocerebral lobes of the brain. They are made 
up entirely of ganglion cells, show no central substance, and stain more 
deeply than the surrounding tissues. In no case has any connection 
