MORPHOLOGICAL EFFECTS OF CROWDING 327 



just been described for Locusta migratoria and L. dancia. In addi- 

 tion Uvarov, using specimens sent him by Faure, discovered dif- 

 ferences in wing venation. With both Locustana and the Locusta 

 we have been discussing, these characters are subject to great varia- 

 tion, and intermediate forms occur. Adults of the desert locust 

 Schistocerca flaviventris have a distinctly higher crest of the pro- 

 notum than those of its supposed gregarious phase, usually known 

 as S. gregaria. The coloration of the hoppers of the two phases for 

 all three series is suggested in Figure 35 and may be compared with 

 the description for the Locusta forms given above. The solitary 

 nymphs are like Locusta danica, while the gregarious nymphs might 

 be mistaken for L. migratoria, since they are of the same color and 

 pattern. 



The evidence that these phases of particular species may be 

 transformed from one to the other does not as yet appear entirely 

 conclusive. It does strongly suggest that such transformations may 

 take place, and for that reason this relatively large amount of space 

 has been devoted to the consideration of these locust phases. 

 Uvarov observed in 191 2 in the northern Caucasus that a swarm 

 composed entirely of L. migratoria deposited eggs in nature in posi- 

 tions that were marked by those engaged in locust control work. 

 The following year the hoppers were mainly of the parental type, 

 but there was a considerable admixture of L. danica nymphs which 

 showed the tjrpical behavior of non-gregarious hoppers. There were 

 many nymphs intermediate between the two. Similar field observa- 

 tions were made in the two following years in a different locality. 



Plotnikov (1924; and, vide Uvarov, 1915, 1927) has carried on 

 rearing experiments of the L. migratoria and L. danica nymphs. The 

 account of the most convincing of his experiments that have come 

 to my attention is summarized here. On May 26, he took 80 larvae 

 of the third nymphal stage, and with typical migratoid coloration, 

 from an ordinary cage of 0.02 cu. m. volume and transferred them 

 to an open-air ground cage which covered 4 sq. m. of surface and 

 was 60 cm. high. An equal number of similar larvae were left in the 

 original cage for controls. After a time the larvae in the ground cage 

 began to turn green, which Plotnikov regards as an intermediate 



