MOVEMENT OF INSECTS 127 



paratively small part in locomotion and act mainly as 

 balancers. Crocodiles also swim by the lasliino- of lluir I ail, 

 but tiu"tles and tortoises use their limbs. 



Many animals move by jumping. A group of lowly insects 

 called springtails have a mechanism very much like that 

 which enables toy wooden frogs to jump from the ground. 

 The extraordinary predominance of insects is shown by the 

 fact that the British Museum contains 3,500,000 specimens of 

 insects and only 1,500,000 other invertebrates ; the latter cover 

 the enormous classes of protozoa, coelenterates, worms of all 

 sorts, Crustacea, spiders, millipedes, mollusca, star-fish, and 

 many other smaller groups. Not only are insects by far the 

 most numerous animals both in number of species and of 

 specimens, but they are relatively the strongest. 



The muscles of the wings of insects contract far more 

 rapidly than any other muscles known amongst all animals. 

 It is held by a good many authorities that the buzzing of the 

 mosquito is due to its wings, and certain experiments have 

 been made upon the note emitted by both sexes. It was 

 found that the males gave a higher-pitched note than the 

 females, and that the note was higher in both sexes when 

 they had fed; the greater the meal, the higher the note. This 

 I have also noticed at "bump suppers" and City dinners. Of 

 four unfed females three gave notes within a quarter of a tone 

 of 264 {i.e. of 240 to 270 vibrations per second), the fourth 

 female gave an abnormally low note of about 175 vibrations. 

 Four other females were arranged in the order of the distension 

 of the abdomen by food, the last being largely distended ; these 

 gave notes corresj^onding roughly to 264 — 281 — 297 — 317 

 vibrations or according to the musical scale, the notes: 



i 



s 



-^^ 



"2;:?" 



:^, 



m 



Three unfed males gave exactly the same note, viz. corrc- 



i 



sponding to 880 vibrations ^ ) |j Immediately after 



feeding one gave the note A^, another which had fed well B-. 



