NO. 1 8 



SENSE ORGANS OF COLEOPTERA — McINDOO 



55 



nalis. The earlier papers concerning the chemoreceptors of Coleoptcra 

 are reviewed by Deegener (see Schroder (y2, pp. 1 50-1 51). Since 

 Minnich's papers on the taste organs of butterflies and flies have 

 recently been reviewed by the writer (47, pp. 36-39), they will not be 

 discussed here. The reader should know, however, that according to 

 the experiments conducted by Minnich certain butterflies bear so- 

 called taste organs in their tarsi, and certain hairs on the proboscis of 

 the blowfly serve as gustatory organs. The most recent paper by 

 Minnich (55) discusses the chemical sensitivity of the legs of a 

 blowfly. 



The writer (46) described and illustrated many tiny peglike hairs 

 found on the cotton boll weevil, but did not attribute a gustatory 



THr 



Fig. 17. — Internal anatomy through tip of maxillary palpus of adult Mexican 

 bean beetle, showing following : Hyp, thick hypodermis ; PH. pseudohairs ; I'l. 

 soft plate; Po, gland pore connected with gland cell, which lies some distance 

 from pore; SC. sense cells; St, tactile hairs; and THr, so-called taste hairs. A, 

 drawing, two-thirds diagrammatic, X300; and B, semidiagrammatic, X 500. 



fimction to any of them. According to jxjsition, and possibly to struc- 

 ture, the ones on the tips of the labial and maxillary palpi are best 

 suited to be taste organs. The same type of hairs was also found at 

 the same place on both adult and larva of the Mexican bean beetle 

 (figs. 14-17, THr). The ones at the tip of the maxillary palpus of 

 the adult (fig. 14, B) are the most numerous and most conspicuous 

 of any yet observed by the writer, and consequently they would appear 

 to have some function other than that of touch. These tiny, thin- 

 walled, and transparent hairs arise from a slightly convex plate, which 

 is soft, flexible, and transparent. The number of hairs on the organ 

 illustrated in figure 17 is about 447. An oblique cross section through 

 the fourth or terminal maxillary segment is represented by figure 17, 

 5 



