A. J. Grove 
457 
made, and the alimentary, tracheal, and nervous systems had been almost 
completed, the work was interrupted by my taking up an appointment in 
India. On returning to England in 1915, the enquiry was resumed for a short 
period at the end of the year, but early in 1916 it had to be abandoned again 
to meet the superior claims of entomological work with the Forces in Mesopo¬ 
tamia, for the War Office. This, and other investigations connected with 
problems which have arisen in England in consequence of the War, prevented 
any further progress being made, but, with the declaration of the Armistice 
it was felt that attention might once more be given to it. In the limited time 
which could be devoted to the work, it has not been possible to carry out the 
original plan of including the whole anatomy in one paper, and the description 
of the head and mouth parts has been selected because of the somewhat novel 
considerations which have arisen in connection with the latter, particularly 
with regard to the function of the labium during the operation of piercing, 
the publication of which it seemed undesirable to delay further. 
The initial stages of the work were assisted by a grant from the Endow¬ 
ment of Research Fund of the Birmingham Natural History and Philosophical 
Society, for which I wish to express my thanks to the Trustees; and I am also 
much indebted to Professor F. W. Gamble, F.R.S. for help and advice. 
METHOD. 
The material used was obtained from apple orchards around Redditch. 
The fixative which was found to give the best results was a very hot solution 
of picro-sulphuric acid according to the following formula: 
Distilled water 100 c.c. 
Sulphuric acid 2 c.c. 
Picric acid to saturation. 
Other fixatives, such as Petrunkewich’s modification of Gilson’s fluid, 
were tried, but were not so successful. An additional advantage of the picro- 
sulphuric solution is that the chitin takes up the picric acid strongly so that it 
appears in the sections stained a deep yellow colour which renders the chitinous 
parts easily distinguishable. The usual series of transverse, longitudinal 
horizontal, and longitudinal vertical sections were prepared, and stained with 
Erlich’s haematoxylin. In addition to the serial sections, dissections and 
preparations of the chitinous parts of the head were made, after treatment 
with caustic potash. The figures were all drawn from the sections or pre¬ 
parations by means of the Camera Lucida. 
NOMENCLATURE. 
During recent years, considerable discussion has arisen regarding the 
homologies of the cephalic skeleton and mouth parts of Hemiptera. The pro¬ 
gress of the controversy has been summarised by Awati (1914) and Davidson 
(1914) so that there is no necessity to give a further summary here in detail, 
