A. J. Grove 
485 
has been indicated in the case of the connection between the pharynx and the 
suction-canal, the maintenance of the parts in the correct relation to one 
another to effect this continuity is brought about by the enclosing of the 
maxillary setae within the channel formed between the epipharynx and the 
maxillary sclerites, which results in their being held firmly in juxtaposition 
with the end of the hypopharynx; and as the orifice of the pharynx is imme¬ 
diately dorsal to the hypopharynx and that of the efferent salivary duct is at 
its tip, it follows that the former will be directly opposite to the suction-canal 
and the latter to the efferent salivary canal. Also, since the maxillary setae 
pass out of the head one on either side of the hypopharynx, and the whole 
apparatus is maintained in a condition of stability by the action of the oral 
muscles, the hydrostatic continuity of the two salivary channels will be 
established, and fluid ejected from the salivary pump through the efferent 
salivary duct will pass uninterruptedly down the efferent salivary canal. The 
presence of fluid around the junction of the two channels will, by its sealing 
action, also assist in effecting this continuity. 
CONCLUSION. 
The method by which the operations of piercing and sucking are performed 
in the Hemiptera is a subject of great interest, and the conditions which have 
been revealed by the study of the head and mouth parts in Psylla mali, are 
such that the working of these parts during these operations is not understand¬ 
able by the hitherto accepted explanations. A method by which these results 
are attained in this insect has therefore been suggested, which, although 
referring strictly to P. mali, presents possibilities which may be capable of a 
wider application, and opens up a field of research, along similar lines, into 
the conditions which obtain in other forms, especially the more specialised 
ones, such as the Chermidae and Coccidae, which should be fruitful of results. 
Unfortunately, in P. mali, the way in which the labium is buried between, 
and hidden by, the procoxae, precludes confirmation of the suggestions by 
direct observation, but, possibly, investigations with other forms may throw 
further light upon the subject. 
LITERATURE. 
Aw ati, P. R. (1914). The Mechanism of Suction in the Potato Capsid Bug, Lygus pabulinus 
Linn. Proc. Zool. Soc. 1914 (2), 685-733. 
Bugnion, E. and Popoff, N. (1911). Les pieces buccales des H6mipteres. Arch. Zool. Paris, 
(ser. 5) vn. 643-674. 
Burdon, E. R. (1908). Some Critical Observations on the European Species of the Genus 
Chernies. Journ. of Econ. Biol. n. 119-148, Pis. VIII, IX. 
- (1905). The Pineapple Gall of the Spruce. A Note on the Early Stages of its Develop¬ 
ment. Proc. Camb. Phil. Soc. xm. 12-19. 
Comstock, J. H. and Kocchi, Ch. (1902). The Skeleton of the Head of Insects. Amer. 
Nat. xxxvi. 13-43. 
Cragg, F. W. (1913). Studies on the Mouth Parts and Sucking Apparatus of the Blood 
Sucking Diptera. Sci. Mem. of the Officers of the Med. and San. Dept, of Govt, of India , 
No. 58. 
