6 4 



ENTOMOLOGY 



make one ; and, in any case, may be determined graphically by 

 means of a kymograph, which, in one of its forms consists of 

 a cylinder covered with smoked paper and revolved by clock- 

 work at a uniform rate. The insect is held in such a position 

 that each stroke of the wing makes a record on the smoked 

 paper, as in Fig. 74. Comparing this record with one made 



FIG. 74. 



Records of wing vibration. A, mosquito, Anopheles. Above is the wing record 

 and below is the record of a tuning fork which vibrated 264.6 times per second. B, 

 wasp, Polistes. The tuning fork in this instance had a vibration frequency of 97.6. 



on the same paper by a tuning fork of known vibration period, 

 the frequency of wing vibration can be determined with great 

 accuracy. As the wing moves in the arc of a circle, the radius 

 of which is the length of the wing, the extreme tip of the wing 

 records only a short mark; if, however, the wing is pressed 

 against the smoked cylinder, a large part of the figure 8 trajec- 

 tory may be obtained, as in Fig. 74, B. The wings of the two 

 sides move synchronously, as Marey found. 



The smaller the wings are, the more rapidly they vibrate. 

 Thus a butterfly (P. rapes) makes 9 strokes per second, a 

 dragon fly 28, a sphingid moth 72, a bee 190 and a house 

 fly 330. 



Wing Muscles. The base of a wing projects into the 

 thoracic cavity and serves for the insertion of the direct mus- 

 cles of flight. Regarding the wing as a lever (Fig. 75, A), 



