Feb.. i893. RESEARCHES ON INSECT ANATOMY. 115 



the Hippoboscidae and in Bvaiila and Nycteribia, elongated in the 

 former and short in the latter group. Miiggenburg supports the gene- 

 rally received view that the true proboscis is formed by the 

 labrum, hypopharynx, and second pair of maxillae (labium). In the 

 Hippoboscidae this organ is long and flexible ; in Braula and Nycteribia 

 it is much shortened, and the formation of its ventral (labial) part by 

 the fusion of a pair of jaws seems very clear (Fig. 2, mx"). In the 

 latter insects, also, the maxillae and their palps are connected at 

 their bases ; the mouth-parts have altogether a more typical aspect 

 than in Diptera generally ; and it would seem that, in the course of 

 the degradation consequent on their parasitic habit, the jaws of these 

 insects have reverted in some degree towards a primitive form. 



Our knowledge of the ears of insects has lately received another 

 contribution. Organs of hearing have not been recognised in many 

 groups, but they have long been known in the jumping Orthoptera, 

 the insects included under the popular terms grasshoppers and 

 locusts. In the short-horned family of these insects, generally known 

 as the Acrididae, but henceforth in accordance with the law of priority 

 to be styled Locustidae,- the organs of hearing are paired, and situated 

 on either side of the first abdominal segment. In the long-horned 

 group, which is called Locustidae by most entomologists, but which 

 we must now learn to know as Phasgonuridae, the ears are placed in 

 the upper part of the tibial joints of the front pair of legs. The tibia 

 is swollen just below the knee, and two slightly curved slits can be 

 seen running longitudinally along the joint for a short distance 

 (Figs. 4, 5). These are the openings into the outer auditory 

 chambers. An account of these remarkable ears has lately been 

 published by Von Adelung (3) who has studied their structure in the 

 genera Phasgonura (Locnsta, auct.), Dectictts, Thavmotvizon, and 

 Meconema. 



The slits mentioned above open into chambers formed by the in- 

 pushing of the integument of the leg. These chambers (Fig. 5) 

 are thick-walled outwardly, but their inner walls are thin, and form 

 the two oval tympana or drums, each of which is in contact with the 

 wall of a trachea, or breathing-tube, the tracheal stem dividing in this 

 region into two parallel branches, whose walls, however, remain in 

 contact. The interior of these air-vessels functions as an internal 

 auditory chamber. Along the outer wall of one of the air-vessels 

 runs a ridge of tissue — the crista acustica — in which are arranged in 

 linear series the cone-shaped endings of the nerve-fibres, each capped 

 by a large cover-cell. These nerve-endings and their cover-cells 

 become successively smaller from top to bottom of the series, which 

 stretches parallel to and about as long as the longer axis of the drum. 



"- This change is less objectionable than many recent revolutions in nomen- 

 clature, as the true locusts, which belong to this family, will henceforth be called 

 Locustidae. Under the former arrangement they were excluded from the family 

 named after them. 



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