

INTRODUCTION. 23 
are said to undergo incomplete metamorphoses, the former com- 
plete metamorphoses. Some never possess wings; indeed, there 
are others which undergo no metamorphosis, and are born pos- 
sessed of all the organs with which it is necessary they should 
be provided. 
Some curious researches have been lately made on the strength of 
insects. M. Felix Plateau, of Brussels, has published some obser- 



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Fig. 16.—Hydrophilus in its four states. 
A, eggs; B, laren: ; C, pupa; D, imago, or perfect insect. 
vations on this point, which we think of sufficient interest to 
reproduce here. 
In order to measure the muscular strength of man, or of 
animals, as the horse, for instance, many different dynamometric 
apparatuses have been invented, composed of springs, or systems of 
unequal levers. The Turks’ heads which are seen at fairs, or in 
the Champs Elysées, at Paris, and on which the person who 
wishes to try his strength gives a strong blow with the fist, repre- 
sent a dynamometer of this kind. The one which Buffon had 

