114 Zoologica: N. Y. Zoological Society lin;3 



d£e, Brenthidae, Bostrychidae, Buprestidae (Agrilus), Cleridse, 

 Trogositidae, Histeridae (Teretrichus), Colydiidse (Colydiumj, 

 Lyctidae, Lucanidse (Ceruchus), Elaterids, Parandridse, many 

 Cerambycidje, Lymexylondidae, etc. This type of body and one 

 more extremely flattened and adapted for living under bark 

 (Cucujus, Brontes) , are very common among the Cucujidae sens, 

 lat. The peculiar conformation of the front and of the mand- 

 ibles of Coccidotrophus and Eunausibius, so strikingly like that 

 of many ants (Cryptocerus, Cataulacus, Colobopsis, etc.) is, more- 

 over, a definite adaptation to guarding elliptical or circular en- 

 trances to solid-walled nesting cavities. It is interesting to note 

 also that the general shape of the body of Coccidotrophus and 

 Eunausibius reappears in several genera of ants which regularly 

 live in narrow plant cavities, e.g., Colobopsis. Simopone, Cylin- 

 dromyrmex, Metapone, Pachysima, Tetraponera and Pseudo- 

 myrma (see Plate III, figs. 1 and 2) . Even the larvae and pupae of 

 these ants have assumed a similar form. (See Wheeler, 1918, and 

 Wheeler and Bailey, 1920). We may say, therefore, that the 

 whole general bodily structure of the various insects I have 

 mentioned has been adaptively modified during their phyloge- 

 netic history and that such a modification can hardly be any- 

 thing but an expression of a concomitant adaptation of their 

 nervous system and reflexes. 



Equally unsatisfactory from an ethological point of view 

 is the reference of other behavioristic peculiarities of the social 

 Silvanids to simple tropisms. Let us take as an example the 

 attraction to the Tachigalia. I agree with Picard (1919) in his 

 contention that phytophagous insects are attracted to their 

 respective host-plants by particular chemical substances in the 

 latter. Entomologists have always believed this but have usually 

 described the phenomena as due to "odor" or "taste." To desig- 

 nate them as chemotropism really adds nothing to our knowledge 

 but a technical term. The ethological question remains : Why 

 is a particular insect species or sex attracted to a particular part 

 of a particular species of host plant, or, in the case of the social 

 Silvanids, why do they fly to and bore into the swellings of the 

 petioles of young individuals of a certain species of Tachigalia? 

 Undoubtedly the exquisite sense-organs in their antennal clubs 

 enable the beetles to detect certain very delicate effluviae emanat- 



