ZOOLOGY AND BOTANY, MICKOSCOPY, ETO. 43 



same function as tlie more highly evolved. It is a fair inference from 

 the nature of the materials composing these organs in insects that 

 they are capable of transmitting vibrations of a high degree of rapidity. 

 To certain objections to the acoustic theory of the functions of these 

 organs it is replied that experiments show that this function in 

 insects is not exclusively owned by the brain and the head, but that 

 the perception of auditory sensations has its seat also in part in the 

 ventral ganglia. 



A. B. Lee * has also examined these organs in a number of Dipteran 

 larvae. He finds that, as a rule, there is one compound (polyscolopic) 

 and one simple (monoscolopic) organ in each segment ; they are 

 always arranged in a bilaterally symmetrical manner ; the number of 

 elements in the compound organ is generally 3, but may be 2, 4, or 5. 

 In opposition to the received view that the nerve-endings are rod-like 

 bodies, consisting of body, head, and point of apex, the apex ending 

 in a chord and the body being traversed by an axial fibre which is 

 the termination of the axial fibre of a ganglion, Lee finds that there 

 is no " apex " to the body, and that the " chord " of Graber's paper 

 is a complex, not a simple termination of a ganglion-cell, that 

 the axial fibre does not belong to the chord, and that the whole 

 rod is to be regarded as a capsular investment of a swollen nerve- 

 ending, and not as the nerve-ending itself. The appearances of 

 " apex " and " chord," so often seen, are j)roduced by certain con- 

 ditions of the tubular wall, termed by Lee " apical tube," which is 

 continued beyond the ends of the rods, hence the chord is made up of 

 an axial fibre and an apical tube ; this is the case with all the auditory 

 rods examined. The axial fibre ends in a hollow bulb at the distal 

 end of the head of the rod in the larva of Simulium. The head of 

 the rod consists of two segments in all examples which were studied, 

 the proximal division having the form of a truncate cone, the distal 

 that of a perfect cone ; the alleged cylindrical and conacoid foi'ms 

 appear from experiments to be due to imperfect resolving power in 

 the Microscope employed ; or, in the case of the conacocephalic form, 

 to a delicate membrane which bridges over and conceals the angle 

 between the body and its shoulder. Lee comes to the conclusion that 

 what Graber describes as distal prolongations of the heads, from which 

 the ideas implied in amphinematic and mononematic are derived, 

 have no real existence, but that the appearance is produced by the 

 lumen of a tube prolonged forwards from all around the head, and 

 attached distally. 



Number of Segments in the Head of Winged Insects.f — The 

 statements concerning the number of segments which form the head 

 of insects are very conflicting ; thus, while Burmeister only recog- 

 nizes two, Strauss-Durckheim allows as many as seven. Dr. A. S. 

 Packard, jun., from the study of the embryos of a great many types, 

 considers that four segments are always to be found, the appendages 

 corresponding to these being the antennae, mandibles, first maxillae, 



* Loc. cit., xxiii. (1883) pp. 133-9 (1 pi.). 



t Amer. Natural., xvii. (1883) pp. 1134-8 (1 fig.). 



