720 Mr. Gilbert J. Arrow on 



sex alone, although belonging to an altogether different 

 tribe, the Heteromera, nlso prodiu e the sound by the same 

 means, viz. friction between the elytra and the terminal part 

 of the abdomen. In many weevils in which Mr. Gahan 

 found curious differences of structure between the sexes 

 the apparatus is also found in the same situation. It has 

 been supposed that such sexual differences pointed to 

 the development of the vocal faculty in the males by the 

 operation of female preference, but I think this striking 

 coincidence of situation in all the known cases, although 

 occurrmg in quite unrelated groups of beetles, clearly 

 indicates that the explanation is the simpler one of the 

 different functions in male and female respectively of the 

 region of the body upon which the organs are here found. 



In another peculiar Dynastid genus, Golofa, the pro- 

 pygidial files have a form slightly different from that 

 occuiTing elsewhere. The segment bearing them, like the 

 rest of the body, is covered with thick hair, and the files 

 are the only denuded portions and are therefore very 

 conspicuous. They are alike in both sexes, but are not, 

 as in other genera, straight and diverging, but each has 

 an outward curvature, thus ( ). In Pscudosyrichthus clatJi- 

 ratns, hairs also surround the files, which are straight in 

 that insect. In Megaccras, which is nearly related to 

 Orydes, the two files are united near the anterior margin 

 of the propygidium and diverge strongly towards the 

 other end. 



A rpiite different apparatus appears in Ligyrus, a genus 

 otherwise closely related to Hctcronychus. Here, a finely- 

 sculptured area is found inside each elytron near its ex- 

 tremity and at the outer edge. The pattern of this is very 

 peculiar, the ridges being seen under the microscope to 

 be blunt-edged and connected by cross- veins so as to form 

 a kind of honeycombed structure. The margin of one of 

 the dorsal segments is sharply upturned on each side 

 beneath these elytral surfaces. Although not suited for 

 producing a musical note, this is probably a true sound- 

 producing organ. Some of the species of Ligyrus, which 

 are inhabitants of Tropical America, are very abundant, 

 and it should be easy to test their vocal power. The 

 occurrence of peculiar adaptations such as this, confined to 

 very small groups or even single species, is one of the most 

 curious phenomena encountered in connection with 

 stridulating organs. 



