748 Mr. Gilbert J. Arrow on 



having acquired a remarkably imiform exterior, charac- 

 terized by great elongation and flatness, whereas the 

 Geotrupidffi, in response to quite different habits, have 

 acquired an equally characteristic rotundity. It is there- 

 fore to the larvfB that we must look for the best evidence 

 of relationship. I have referred to the very striking fact 

 that the stridulating organs of both larval and adult 

 Passalidte are highly-developed phases of rather simpler 

 structures occurring in the corresponding stages of Geo- 

 trupidffi. In the larva of Gcotrupes the third pair of legs 

 is much reduced in size and directed forwards in such a 

 way as to scrape a pair of files at the bases of the inter- 

 mediate legs. In the Passaliclre these files again appear, 

 and the modification of the last pair of legs has advanced 

 to such a degree that they seem to be mere jointless 

 rudiments. It is scarcely rash to prophesy that examin- 

 ation of the yet unknown larvae of other genera of these 

 groups will reveal intermediate stages in the transition. 

 No apparatus has been found in any other group bearing 

 any greater resemblance to this type than that of the 

 larval Lucanidse, in which the hind-legs are not at all 

 reduced and themselves bear the file upon the greatly 

 enlarged trochanter. Although the action is similar 

 the structure is widely different. In all other known 

 Lamellicorn larvae the organs are borne, not upon the 

 legs but the jaws. This single fact therefore, apart from 

 other evidence, affords almost conclusive proof of the 

 relationship between the Geotrupidte and Passalidfe. But 

 the vocal apparatus of the adult beetles points in the 

 same direction. It is at last established, after much 

 debate, that the Passalid beetle stridulates by the opposi- 

 tion of certain stout spines upon the wings to other spines 

 studding a pair of bosses situated upon the antepenulti- 

 mate dorsal segment. In the Geotrupidse again we have 

 found in Geotrupes and Bolhoccras sound-producing spines 

 upon the terminal dorsal segments and corresponding 

 spines upon the wings, and in Ochodc'&us I have described 

 highly peculiar paired projections upon the antepenulti- 

 mate dorsal segment, to which no other analogues can any- 

 where be found but the bosses upon the same segment in 

 the Passalidae. Although the musical ajDparatus affords 

 the most striking evidence of this unexpected relationship, 

 corroboration is supplied by various other features. Thus 

 in the perfect insects the configuration of the head and 



