278 



On the Spiracles of Coleoptera and on the Sound Pro- 

 duced by Polyphylla. 



On 10 July 1874 I observed a male Polyphylla variolosa 

 (Hentz) making a creaking noise while moving its abdomen up 

 and down under the elytra. Examination of the specimen 

 shows upon the outer face of the spiracle-bearing plate of the 

 metathorax an oblong, slightly swollen area, free from pubes- 

 cence, of a thin texture and pale color. This is covered by the 

 elytra when the insect is at rest. At a corresponding point 

 under the margin of the elytra is seen an area of similar size 

 and of a pink color. The same structure is to be seen in the 

 female Polyphylla, but what relation, if any, this has to the 

 production of the sound it is difficult to understand. 



The existence of mesothoracic and metathoracic spiracles in 

 coleoptera has recently (^Amer. Nat., 1874, p. 532) been ques- 

 tioned, because of the absence of such spiracles in the larva. 

 None are ajiparent upon the mesothorax of Polyphylla, but a 

 more careful examination will discover that they are present 

 here, since Strauss-Durckheim found them in Melolontha and 

 Reinhard asserts their existence in the hymenoptera, notwith- 

 standing that they are not externally visible. The metathoracic 

 spiracles, however, are very obvious in Polyphylla, being placed 

 at the inner margin of the membrane which forms part of the 

 dorsal face of that plate which on its vertical face presents the 

 structure noticed above. Behind these spiracles are situated 

 seven additional pairs, a pair upon each segment of the abdo- 

 men excepting the last. The spiracles of the prothorax and of 

 the basal segment of the abdomen are larger than the others, 

 although, being concealed in the sutures, they are to be found 

 only by dissection. In Tenebrio, and many other coleoptera, 

 it is true, no metathoracic spiracles are apparent. 



Dr. Packard states (1. c.) that in the coleoptera there are 

 usually eight pairs of abdominal spiracles. This is manifestly 

 incorrect in regard to the imago, for in no adult hexapod insect 

 can more than seven pairs of abdominal spiracles be demon- 

 strated. In larvae eight ])airs is the maximum, hut functionally 

 the eighth pair belongs to the seventh segment and the first 



