NOTES ON THE MYIASIS-PRODUCING DIPTERA. 



257 



The shape of the mandibular sclerites and the fulcrum (pharyngeal sclerite) is 

 very characteristic in the third stage larvae of the different genera of the higher 

 Diptera. In fig. 1 (ci-d) the cephalopharyngeal skeletons of the third-stage 

 larvae of Musca nehulo, Calliphora crythroccphala, Lucilia sericata and Sarcophaga 

 are illustrated, all being drawn to the same scale. The differences are obvious, 

 and therefore I do not intend here giving a detailed description of them. It is, how- 

 ever, necessary to point out that in the case of the larvae of C. crythroccphala and 

 Lucilia sericata the differences are small, but nevertheless sufficient to determine the 

 species. I will on another occasion deal at length with the structure of the cephalo- 

 pharyngeal skeletons of a number of the larvae of the higher Diptera. I would, 

 however, like to point out that in the larva of Musca and allied genera there are always 

 two mandibular hooks, and not one, as is usually stated in the books and papers on the 

 subject. This error is no doubt due to the fact that the left hook is shorter and 

 narrower than the right, and is therefore easily overlooked. It is a valuable diagnostic 

 character in this group. 



Anterior spiracles. The anterior spiracular openings are always situated at the 

 sides of the lower border of the apparent third segment. Each consists of a fan-shaped 



^#^^ 



Fig. 2. — Anterior spiracles of third-stage larvae of: {a) Musca 



domestica ; (6) M. nehulo ; (c) Calliphora erythrocephala ; 



(d) Lucilia sericata ; {e) Sarcophaga sp. 



chitinous structure with a varying number of small finger-like processes at the apices 

 of which there are oval openings. These openings lead into a miniature vestibule, 

 which is continuous with a large trachea ; in the majority of the third-stage larvae the 

 anterior spiracles are functional. They are always absent in the first-stage larva, 

 and appear only in the second instar. Although there is great variation in the number 

 of the finger-like projections in the same species, and even in the same larva, these 

 structures are very useful for diagnostic purposes when taken along with the charac- 

 ters of the posterior stigmata and the cephalopharyngeal skeleton. In the third- 

 stage larva of Musca domestica (fig. 2, a) there may be five, six, or seven processes ; 

 in M. nehulo (fig. 2, h) seven or eight; in Calliphora erythrocephala (fig. 2, c) ele^^en or 



