336 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, 1 37 



The musculature of the mesothorax of Anisopus was investigated 

 mainly by dissection under the binocular dissecting microscope. A 

 bold snip with the scissors will split the fly easily down the median 

 dorsoventral line, and one or the other half will usually contain such 

 things as the median furca. Figures 2, 3, and 4 show the steps in a 

 dissection of a half mesothorax ; dissections from other approaches 

 were made when investigating the relationships of particular muscles. 

 Most dissections were made of specimens fixed in chlor-picro-acetic 

 fixative ^ and stored in 70-percent alcohol. This fixative stains the 

 tissues slightly yellow and it also causes transverse shrinkage of 

 muscles, thus separating them from each other when they are con- 

 tiguous ; it does not cause them to break away from their attachments 

 until dislodged with a dissecting instrument. 



Grenacher's alum-carmine stained the small pleural muscles satis- 

 factorily both for dissection and for making transparent whole mounts 

 for examination under the compound microscope. Serial sections 

 were made of a few specimens. 



Perusal of recent papers on the musculature of Diptera, e.g., Bon- 

 hag (1949) on Tabanus, Miller in Demerec (1950) on Drosophila, 

 shows that recent workers on the anatomy of Diptera have not found 

 any of the proposed muscle nomenclatures completely acceptable ; 

 nor did Maki (1938) at an earlier date, though there are common 

 lines running through the systems of Snodgrass, Maki, and others. 

 The explanation of this state of affairs is obvious ; all three thoracic 

 segments in Diptera are so much modified that sooner or later a 

 muscle is encountered that cannot be homologized satisfactorily with 

 those in other thoracic segments — still less with any of the proposed 

 master systems. 



I propose to group the muscles of the mesothorax as shown in 

 table I. Below, in this paper, the muscles are treated consecutively. 

 In figure 4 they are labeled with the numbers they have in the 

 grouping system. 



The names used for the muscles in Snodgrass's (1935) general 

 terminology, in that of Ritter (1911) for Calliphora, that of Maki 

 ( 1938) which was a general terminology applied to five different Dip- 

 tera along with many other insects, Bonhag's (1949) used in his 

 paper on Tabanus, and Miller's used in describing the musculature of 



3 60 cc. of a i-percent solution of picric acid in methylated spirits (i.e., approx. 

 9S-percent alcohol) ; 10 cc. of chloroform ; 5 cc. of acetic acid. Specimens left in 

 fixative for 12 hours or overnight, then washed and stored in 70-percent 

 alcohol. 



