302 THE PRACTICAL APPLICATION OF ECOLOGY 



THAN SI ENS 



simulate that of the immediate environment. The adults have 

 the pronotum somewhat arched with an evident longitudinal 

 carina : there is no marked constriction and the pronotum is 

 relatively longer than in the gregarious phase. The hind femora 

 are also relatively longer and the tegmina shorter. The diagnostic 

 ratios are given in the table above. 



The phasis transiens is not represented by any definite form, 

 but by a continuous series of transitional forms between the 

 solitary and gregarious phases. Such a series may be observed 

 either {a) when the transformation is from the solitary phase 

 towards the gregarious phase, when it may be termed phasis 

 congregans ; or (b) when the tendency is in the opposite direction, 

 when it is termed phasis dissocians. These two phases are 



essentially of a biological nature, 

 but it appears that it may be 

 possible to distinguish them also by 

 minor details of structure and colour. 

 In the accompanying diagram the 

 GREGARiA general scheme of cyclic inter- 

 relations between the four phases 

 just described is represented. It 

 must be pointed out that the phasis 

 transiens may be represented by 

 forms morphologically and bio- 

 logically quite close to either p. solitaria, or p. gregaria, into both 

 of which the series merges almost imperceptibly. 



Under experimental conditions, given the right combination of 

 temperature and humidity, plenty of sunlight and adequate 

 suitable food, it is easy to rear locusts in one or other of their 

 phases. If the newly hatched nymphs are reared under crowded 

 conditions, they show all the main features of the phase gregaria, 

 although it is doubtful whether absolutely typical gregaria are 

 always produced under these conditions. Under less crowded 

 conditions the locusts develop into phase transiens, while if each 

 early nymph be reared in a separate container it develops into 

 solitaria. Faure (1932) showed clearly that in this phase the 

 individual nymphs assume a coloration more or less resembling 



SOLITARIA 



