9 
Siphonoph ora rosarum 
and the presence of certain sense organs not present in the apterous 
form. These points are summarised at the end of the paper. 
I wish again to express my gratitude to Mr A. E. Shipley, F.R.S., 
and Mr L. Doncaster for help given during the progress of the work, 
and to Professor F. W. Gamble, F.R.S., and Dr C. Gordon Hewitt for 
kindly reading and revising the manuscript. 
Method. 
The insects were fixed in exactly the same way as was stated in 
Part I, and the usual serial sections obtained. 
The winged stage being so much smaller than the apterous stage, 
the difficulties of actual dissection were materially increased, and this 
method had finally to be abandoned. In order to obtain figures of the 
nervous system and alimentary canal, reconstructions had to be made. 
In the case of the nervous system, the greatest transverse measurement 
of the nervous system in each of the sections of a complete series was 
obtained by means of the camera lucida. These distances w r ere then 
plotted out on squared paper—one half on each side of a middle line. 
The distance along the middle line between any two of the measure¬ 
ments represented the thickness of the sections at the same magnifica¬ 
tion at which the measurements were taken. By joining up the points 
thus obtained, a plan of the nervous system resulted. For the alimen¬ 
tary canal a different method was adopted. Each part of the alimentary 
tract was considered separately, and the number of sections counted in 
which the different portions appeared. The figures thus obtained 
represented the relative lengths of the various divisions; and having 
determined the transverse dimensions at the magnification at which the 
reconstruction was to be made, a semi-diagrammatic drawing, to scale, 
was made on squared paper. Text Figs. 1 and 2 (p. 7) are the average 
result of several such sets of figures obtained from several complete 
series of serial sections. 
The External Characters. 
Buck ton’s (1875-1882) figure and account of the winged stage of 
S. rosarum seem to contain some small inaccuracies when compared 
with the actual specimens. These inaccuracies will be dealt with in the 
general description. His diagnosis is as follows: 
“Green, not bristly. Heads and thoracic lobes black. Abdomen with six or 
more black transverse bars, decreasing in length and breadth towards the apex. 
