322 



ANIMAL AGGREGATIONS 



wide that the extreme forms have been recognized as distinct 

 species." These diverse forms of apparently related stock Uvarov 

 calls "phases." 



Fig. 32. — Showing morphological differences between phases of different species of 

 acridid grasshoppers or locusts, i, 2, Pronotum of danica phase of Lociista tnigratoria L. 

 3, 4, Ditto of viigratoria phase of the same. 5, 6, 7, Pronotum and wing of pardalina 

 phase of L. pardalina Walk. 8, 9, 10, Ditto of solitaria phase of the same. 1 1 , Pronotum 

 of gregaria phase of Schistocerca gregaria Forsk. 12, 13, Ditto oi flaviventris phase of the 

 same. (After Uvarov 1928, by permission of the Imperial Bureau of Entomology.) 



Uvarov was led to this theory of phases by a consideration of the 

 interrelations between the two supposedly good species, Locusta 

 migratoria and L. danica. In his early work, on account of distinct 



