March, 1905.] Powell : Wings of Certain Beetles. 15 



Among the Hymenoptera I have found the metathoracic spiracle 

 present in the larva? of the honey bee, Apis mellifica, of a wood-bor- 

 ing wasp and of an undetermined mud-wasp. In all cases this spira- 

 cle is not to be distinguished from the other spiracles of the body, 

 either in shape, size or position. 



I have also found vestiges of the metathoracic spiracle present in 

 the larva of the silk-worm, Bombyx mori. 



In the Neuroptera I have found the metathoracic spiracle present 

 and open(?), though small, in the larva of Raphidia sp., and also in 

 the pupa. 



There are numerous references in entomological literature to two 

 pairs of thoracic spiracles. Among the Coleoptera both meso- and 

 metathoracic have been recorded for the larva of Ehnis (Parnidas) and 

 Lycus (Lampyridas) (Packard). In the Hymenoptera both pairs are 

 present in the Aculeata and in the Siricidse, though in the latter the 

 metathoracic is sometimes closed. Both spiracles are also present in 

 Apis and Hylotoma (Packard). Packard figures the larva of Bomb us 

 with a full-sized metathoracic spiracle and Bugnion has done the same 

 for Encyrtus fuscicollis. Packard also figures a meso- as well as a meta- 

 thoracic spiracle in a locust, Melanoplus femur-rubrum. Calvert 

 (1893) has found that in all the adult Odonata the metathoracic 

 spiracle is present and very distinct. In those insects, the larval 

 stages of which are passed in the water and which develop tracheal 

 gills (Odonata and Ephemerida), thoracic gills are present and open 

 in the early larval stages, but later become closed (Packard). Both 

 pairs of spiracles have been shown by various authors to be present in 

 the Hemiptera. Among the Diptera both pairs are present in the 

 larvge of Bibionidse and Cecidomyidae (Miall and Hammond). Both 

 pairs are present in the Termites. 



2 . The Position of the Thoracic Spiracles and their Relation to 

 the Wing Discs. 



During embryonic life the spiracles are formed as invaginations on 

 the pleurae of their respective segments at a point nearly midway 

 between the middle of the segment and the suture in front of it. This 

 embryonic position of the spiracles can be readily seen by reference to 

 the figures of Graber (1891) who worked on the embryonic stages of 

 the Lepidoptera, Coleoptera and Orthoptera and the figures of Wheeler 

 (1889) for the Coleoptera. The mesothoracic spiracle often migrates 



