456 
✓ 
THE ANATOMY OF THE HEAD AND MOUTH PARTS 
OF PSYLLA MALI, THE APPLE SUCKER, WITH SOME 
REMARKS ON THE FUNCTION OF THE LABIUM. 
By A. J. GROVE, D.Sc. 
University of Sheffield. 
(With Plates XXVI—XXVIII and one Text-figure.) 
CONTENTS. 
PAGE 
Introduction .. . 456 
Method . . . . . • . . . . / . • 457 
Nomenclature ........... 457 
The Exoskeleton of the Head ........ 460 
The Head Capsule ..460 
The Buccal Region and Labium.460 
The Setae.464 
The Hypophar 3 7 nx ......... 467 
The Endoskeleton of the Head ..467 
The Tentorium . .467 
The Salivary Pump.468 
The Pharynx.. 469 
The Musculature of the Head ........ 469 
I. The Antennal Muscles.469 
II. The Pharyngeal Muscles ....... 469 
III. The Pump Muscle.470 
IV. The Supporting Muscles of the Tentorium .... 470 
V. The Musculature of the Setae . . . . . . 471 
VI. The Muscles of the Head Capsule and Neck . . . . 471 
VII. The Muscles of the Oral Region.472 
VIII. The Muscles of the Labium . . . . . . . 472 
IX. The Muscles of the Labial Furrow ..... 473 
The Mechanism of Piercing . . . . . . . . 473 
The Mechanism of Suction ......... 482 
Conclusion ..485 
Literature 485 
Explanation of Plates ......... 487 
Reference Lettering ..488 
INTRODUCTION. 
The investigation, of which the results contained in this paper are a part, was 
first commenced in 1910. It was then proposed to describe in some detail the 
entire anatomy of the adult insect, but when a measure of progress had been 
