1922] Cramp*on — Relationship of Hemiptera-Hotnoptera 31 



between the first branch of radius and the anterior margin of the 

 wing, as well as a tendency for Rs to turn forward toward the 

 anterior margin of the wing. In order to make the series include 

 as wide a range of types as possible, I have included some of the 

 most specialized types as well, and, as one may see by com- 

 paring Figs, 17 and 19, in which radius and media are practically 

 the only veins retained in a well develped condition, there is 

 Si marked parallelism in the more highly specialized members 

 of the two groups, as well as in the intermediate and more 

 primitive representatives of the Psocids and Homotera, This 

 parallelism in a wide range of wing types, as well as in a multitude 

 of structures from all parts of the body, can be explained only 

 as the result of the operation of the same developmental ten- 

 dencies (i.e. the expression of the presence of the same genes, 

 determinants or factors — albeit these are modified to some extent 

 in the derived groups by the influence of other factors) inherited 

 from a common ancestry. 



From the foregoing facts, I would conclude that the Psccids 

 and Hemiptera-Homoptera were descended from very similar 

 ancestors, and since the Psocids were apparently descended from 

 ancestors closely resembhng the Protorthoptera in many res- 

 pects, it naturally follows that the ancestors of the Homoptera 

 must also have resembled the Protorthoptera in many respects. 

 The fact that the saltatorial Orthoptera, which are the modern 

 representatives of the Protorthoptera, have likewise retained 

 many features suggestive of affinities with the Hemiptera- 

 Homoptera is also in harmony with such a derivation of the 

 Homoptera; but there are other factors involved, which further 

 complicate the question of the origin of the Homoptera. The 

 primitive type of venation exhibited by the fore wing of the 

 Homopteron Hotinus sp., figuj'ed by Handlirsch, 1909, appears 

 to be of a lower type than that of most Protorthopterous fore 

 wings, and suggests affinities with the Neuroptera and Proto- 

 blattids. The venation of the Homopteron Onneiu's is also very 

 suggestive of that of certain Neuroptera such as Psychopsis, 

 particularly in the peculiar arrangement of certain small cross 

 veins which unite end-to-end to form a paramarginal line extend- 



