MORPHOLOGICAL EFFECTS OF CROWDING 331 



report, record that they considered and rejected the possibihty that 

 the offspring from the breeding swarms of M. spretus change in the 

 dir':^ction of a morphologically related species, M. atlanis, which 

 differs from M. spretus by being less gregarious in its habits. The 

 nymphs of the latter have coloration suggesting that of other typical 

 swarming-hoppers, and the pronotum of the adult is proportionately 

 shorter than that of M. atlanis. Somes (1914) questioned on mor- 

 phological grounds the validity of the separation of the two species ; 

 and Parker (1925) and Hebard (1925) have suggested that the two 

 are phases of the same species. This suggestion offers an interesting 

 possibility of putting the whole phase theory to the test of critical 

 experimentation without the necessity of making an expensive, time- 

 consuming journey. 



In final criticism of the phase theory, it does not seem to be clearly 

 proved that the transformations from one phase to another do 

 actually take place on a large scale and to a convincing degree. 

 But as one reads through the descriptions of the different workers 

 from different parts of the world and finds that independent students 

 have thought that they have obtained these transformations, and 

 when one learns that the same suggestion had been considered in 

 1878, long before Uvarov first stated his phase theory, it becomes 

 impossible to dismiss the evidence entirely, although for the time 

 being it must rest with a verdict of unproved but a promising open- 

 ing for further work. 



DROSOPHILA CULTURE EXPERIMENTS 



The work of the Drosophila students probably presents the great- 

 est mass of carefully controlled work upon the culture of a single 

 animal species yet performed. Unfortunately, certain phases of the 

 environment within the culture bottles cannot be controlled, but on 

 the whole these workers have succeeded in creating standard con- 

 ditions for their breeding experiments. For this reason one may ac- 

 cept their results without the mental reservations just indicated in 

 the case of work on the transformation of locusts from one phase to 

 another under laboratory conditions. 



Bridges (192 1) called attention to the necessity of having opti- 



