NO. l8 SENSE ORGANS OF COLEOPTERA — McINDOO 63 



grape sugar, table molasses, corn sirup, and black-strap molasses, and 

 even showed preferences between them. 



Bean foliage, sprayed with arsenicals, was repellent, but not sufifi- 

 ciently so to prevent the leaves from being eaten. Lead arsenate 

 was most rei:)ellent ; magnesium arsenate was less so ; and calcium 

 arsenate was least repellent. Bean foliage sprayed with sweetened 

 arsenicals was more attractive than unsprayed foliage. Bean foliage 

 sprayed with sweetened magnesium arsenate was more attractive than 

 foliage sprayed with nonsweetened magnesium arsenate. This would 

 indicate that it might be of economic importance to use sweetened 

 arsenicals in control measures, particularly to ix)ison the overwinter- 

 ing beetles early in the season. 



In regard to the tropic receptors of the bean beetle, the following 

 may be stated. The structure of the compound eyes and ocelli was 

 not studied, but these organs are normally developed and .seem to 

 function adequately, so far as beetles are concerned. 



Two kinds of so-called smelling organs — certain hairs on the an- 

 tennae, and pores, called olfactory by the writer — are fully described. 

 These hairs appear long and slender, have thin, almost transparent 

 walls, and are connected with the sense cells. They are numerous and 

 lie in five groups on the distal ends of the ninth, tenth, and eleventh 

 segments. The olfactory pores on the adult beetle were found as 

 usual on the elytra, wings, legs, mouth parts, and antennae. The total 

 number counted was only 692. The pores on the larva lie on the head, 

 antennae, legs, and mouth parts. The total number found was only 

 62. The fact that the total number of pores on both adult and larva 

 is comparatively small might be correlated with the fact that this 

 species is " stupid " when olfactory responses are considered. 



A so-called taste organ was found at the tip of the maxillary palpus 

 of the adult. It is a soft plate which bears about 447 tiny, thin-walled 

 sense hairs. The fact that the bean beetle possesses two of these 

 highly developed sense organs helps to explain how these insects were 

 able to distinguish so readily between the various aqueous solutions 

 and insecticides fed to them. 



The only so-called auditory organ found in the bean beetle lies in 

 the second antennal segment. These structures, called Johnston or- 

 gans, were formerly assumed to be auditory in function, but now are 

 believed to be muscular receptors to register the movements of the 

 antennae. 



The remaining receptors described are the tactile hairs, which are 

 widely distributed over the surface of the beetle. 



