LOCUSTS AND GRASSHOPPERS (ACRIDIID&). 103 



of the number of species and the geographical dis- 

 tribution of the migratory locusts. 



On an average, the Rocky Mountain Locust requires 

 about seven weeks, from the time of hatching, to pass 

 through its stages of growth ; and the perfect form is 

 attained through a series of five moults. 



Apart from the colorational, and more minute 

 structural changes which take place with each moult, 

 the most striking change in the course of development 

 is the growth of the wings. We examine the first instar 

 of Caloptenus spretus, the young locust just emerged 

 from the egg and colourless. In the second instar the 

 chief difference is the development of colour ; in the 

 third there is plainly a slight development of the future 

 organs of flight. After the third moult there is a great 

 change ; the instar then .disclosed the fourth has 

 undergone a considerable change in the wing-rudiments 

 or wing-pads, which have become free and detached, the 

 second pair being the larger, and outside the other pair. 

 The fifth instar differs little, except in the increased 

 size of the wing-pads. At the fifth and last moult the 

 instar is the perfect insect, with full free wings, the 

 thorax flattened, the colour different. The most pro- 

 nounced changes, it will be observed, occurred at the 

 third and fifth skin-sheddings, after each of which con- 

 siderable difference in the form of the insect was 

 presented. 



