NOTES ON THE DISTANCE FLIES CAN TRAVEL 



381 



■whose wing musculature appears to have 

 been first explained correctly by Graber. 

 No one has yet, however, fully explained 

 how it is that these insects are able to 

 execute such quick movements. Is it 

 possible that the division of the thoracic 

 muscles into groups, a division that 

 seems to prevail in all the insects that fly 

 in this manner, is a provision by which 

 the muscles act in relays? If we recall 

 the motions that are executed by a 

 single pair of antagonistic muscles, can 

 we recall a single instance where move- 

 ments are executed at the rate of several 

 liundred per second? I doubt if even in 

 those minute forms where there appears 

 "to be the least molecular difficulty — I re- 

 fer to the cilia of microbes — so high a 

 rate of vibration would be claimed. (I 

 know of no investigations.) Few men 

 •can execute more than ten movements 

 -per second with any muscle. 



It has often struck me when examin- 

 ing the batteries of muscle by which the 

 >quick-action insects execute their wing 

 -movements, that here is a mechanical 

 .and physiological problem that it would 

 be well worth while to investigate. 



KNORMOUSLY POWERFUI. WING MUSCLE;S 

 OF FI^IES 



Ten flies of the smaller of the two sar- 

 >cophagous species found common at this 

 Station* were weighed after being chlo- 

 roformed. They were taken as captured 

 in the middle of the day. No doubt a 

 ■slight amount of the vapor of chloroform 

 .added to the apparent weight of these 

 ten flies, which was 478 milligrams. The 

 •central thoracic muscles were removed 

 and weighed, and also the two sets of 

 lateral muscles. The result was 67.5 

 milligrams for the central and 58.5 for 

 the lateral. Thus we have: 



Average weight of fly, 47-83 mg- 



Average weight of lateral batteries of 

 -muscle, 5.85 mg. 



Average w^eight of central battery of 

 •muscle, 6.75 mg. 



Total we\ght of muscles, 12.6 mg. 



From which we learn that the weight 



* Experiment Station of Hawaiian Sugar 

 Planter's Association, Honolulu. 



of the central thoracic muscles is 14. i 

 per cent of the weight of the fly, and the 

 weight of the lateral thoracic muscles is 

 12.2 per cent of the weight of the fly, and 

 that together these thoracic muscles con- 

 stitute 26.2 per cent of the weight of the 

 fly. 



The method was to fix the flies in 50 

 per cent alcohol, dissect out the muscles, 

 soak them in water for several hours, re- 

 move the excess of water and weigh the 

 muscles barely moist. 



Eight females of the coinmonest spe- 

 cies of Syrphiis about the Station had 

 their great thoracic muscles removed and 

 weighed, with the following results : 



Longitudinal muscles, 12.3 per cent of 

 the weight of the fly. 



Oblique muscles, 9.2 per cent of the 

 weight of the fly. 



Total, 21.5 per cent of the weight of 

 the fly. 



A similar trial with ten males weigh- 

 ing 774 mg. gave as a result : 



Longitudinal muscles, 17.12 per cent 

 of the weight of the fly. 



Transverse muscles, 12.5 per cent of 

 the weight of the fly. 



Total, 29.62 per cent of the weight of 

 the fly. 



The males of this species have a 

 greater proportion of muscle than the 

 females. This appears to be generally 

 true of flies. 



The wing muscles of a notable flier, 

 Volucella ohesa, often to be seen, espe- 

 cially in the morning, standing in the air 

 in shady places in Honolulu, were re- 

 moved and weighed in the same manner 

 as described for the two sarcophagous 

 species. The result showed that the lon- 

 gitudinal muscles constitutes 25.7 per 

 cent of the entire weight, while the 

 oblique sets constitute 22.3 per cent of 

 the entire weight, so that together these 

 muscles constitute no less than 48 per 

 cent of the weight of the insect. It 

 should be noted "that all the specimens 

 examined appeared to be males, and the 

 absence of gravid females may in some 

 degree account for the diff'erence be- 

 tween these results and those noted in 

 the case of the sarcophagous flies. How- 



