496 Wisconsin Academy of Sciences , Arts, and Letters. 
water, and it may be that these sacs are used to bring the insect 
to this position. 
Nervous System. —-(PI. XXXV, Fig. 13.) The supra-oesopha- 
geal ganglion is situated in the posterior part of the head; it 
shows dorsally a median longitudinal furrow which makes it easy 
to distinguish a right and a left lobe. From the posterior end 
of each lobe passes a circum-oesophageal commissure, the two 
uniting in the infra-oesophageal ganglion which lies at the ex¬ 
treme anterior margin of the prothorax. The remaining gang¬ 
lionic system of Ranantra is represented by but one other large 
ganglion situated mostly within the mesothorax but extending 
backward for some distance into the metathorax. This single 
thoracic ganglion is connected with the infra-oesophageal gang¬ 
lion by two long, thin cords while from its posterior end arise the 
two nerve bundles which, passing backward, supply nearly all 
parts of the abdomen. 
In a general dissection there: is but little to notice except the 
branches coming from the thoracic ganglion, and the nerves given 
off from the two> main trunks of the abdomen, all of which is 
shown in PI. XXXV, Fig. 13. In a microscopic preparation of 
the entire nervous system, each of the two strands leaving the 
posterior partiof the thoracic ganglion appears single and not di¬ 
vided into parts. After the first nerve has been given off, the 
main strand shows a distinct division into four parallel strands, 
the presence of which is only seen in stained and mounted 
preparations. Soon another nerve is given off and then the 
main branch shows three separate strands for some distance, a 
fourth, however, appearing. These four remain together until 
the next branching, when there appears a division into two parts, 
each containing two of the four strands. This is really a split¬ 
ting of the main nerve, but one is larger than the other and re¬ 
mains as the main trunk, the other appearing as a branch which 
leaves as the other branches have done and passes towards the 
side of the body. Between this branch and the main nerve, the 
oviduct passes. The main trunk with its two remaining strands 
continues towards the posterior part of the body and when the 
next nerve is given off divides so that one strand remains as the 
main nerve and the other passes off as a branch. The single 
strand of which the main nerve is composed divides so that there 
are again two strands in it before the next and last noticeable 
nerve is given off. 
