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XVXII. A Contribution to the Classification of the 

 Coleopterous family Passalidse. By GiLBEHT 

 J. Arrow, F.E.S. 



[Read October 3rd, 1906.] 



The Passalidx form a family which, almost universally 

 distributed and very abundant in the forest regions of 

 the Tropics, is probably as compact and homogeneous as 

 any equally numerous and widely distributed group of 

 animals. As a corollary we find the differences between 

 the component forms very slight and with exceedingly 

 numerous degrees of variation the separation into species 

 is very imperfect. 



Whether the remarkable secondary adaptation of the 

 wings to serve as organs of sound-production is to be 

 regarded as cause or effect, it seems to be the case that 

 their primary function is becoming obsolete, species being 

 found in different parts of the family in which they are 

 already useless for flight. The result is that locomotion 

 has become very restricted and segregation into a multi- 

 tude of local forms, too recent for marked specific 

 differentiation has taken place. 



From their generally large size, general form and 

 manner of life, the Passalid/B could not fail to be associated 

 in the mind with the Lucanid^e, but the generally accepted 

 view that there is a special relationship between the two 

 families I believe, as I have previously stated, has little 

 substantial foundation. A rather striking feature in which 

 the PasscdidiB differ from the LttcanidiB, as from wood- 

 feeding insects in general, is their constancy of size, a 

 phenomenon of which we have recently learnt the probable 

 explanation. Dr. Ohaus has made the very interesting 

 discovery that these insects are not during their early 

 stages at the mercy of the rather precarious circumstances 

 of their environment like others of the same habit of life, 

 but that by a social organisation of a kind new to us among 

 insects they have become to some extent masters of their 

 fate. The Brazilian species studied by this naturalist 

 live in small communities consisting of the two parents 



TRANS. ENT. SOC, LONP, 1906. — PART IV. (jAN, 1907) 



