A. J. (Trove 
9 
The rectum is also very variable in different individuals. When no . 
contraction has taken place, the lumen is rounded in contour, and 
bounded by the usual thin muscular wall. Where contraction has 
occurred, the rectum becomes stellate in cross-section. A sphincter 
muscle, formed by the thickening of the muscular wall, closes the anus 
as in the apterous form. 
The salivary glands are exactly similar to those present in the 
apterous stage, and the ducts take the same curious course round the 
nervous system, uniting in the mid-ventral line, and then continuing 
forward underneath the nervous system to the mouth. 
The Nervous System. 
The comparison of the nervous systems of the two stages is rather 
disappointing, because it would be expected that such a vital difference 
in habit would involve some marked changes in the nervous system. 
The slight differences which are present will be dealt with in the 
description of the various parts. In general appearance, the central 
nervous system (Plate II, Fig. 4) is very similar to that of the apterous 
individuals. The same ganglia, viz., two cerebral ganglia, each with its 
adjacent optic lobe or ganglion, two sub-oesophageal ganglia, three pairs 
of thoracic ganglia, and a single median abdominal ganglion, are present. 
The ganglia are connected up in exactly the same way as is the case in 
the apterous stage, but the whole system appears to be much more 
contracted and concentrated. 
The cerebral ganglia and their optic lobes or ganglia, are larger in 
proportion to the rest of the nervous system. This is, of course, the 
natural outcome of the different habit of the insect in this stage, for it 
is reasonable to suppose that the habit of flight would be accompanied 
by a greater demand upon all the organs of sense, and more especially 
upon the eyes and any organs which are adapted to appreciate waves in 
the air. These organs, placed in close relation with the head, are 
innervated by the cerebral and optic ganglia enclosed in the head. The 
cerebral ganglia are joined to the sub-oesophageal ganglia by a pair of 
circum-oesophageal connectives, which arise, as in the apterous form, 
one from each of the lower and tapering portions of the cerebral ganglia ; 
and passing one on each side of the pharynx, become continuous with 
the sub-oesophageal ganglia. 
The sub-oesopliageal ganglia need no comment other than that my 
investigations have failed to reveal any nerve given off from these 
