1922] Crampton — Relationship of Hemiptera-Homoptera 



35 



The facts brought out in the foregoing discussion would 

 indicate that the ancestors of the Hemiptera-Homoptera arose 

 from forms anatomically intermediate between the ancestors 

 of the Psocids and those of the Neuropteroid insects. In other 

 words, the ancestors of the Hemiptera-Homoptera were apparent- 

 ly anatomically intermediate between the insects forming the 

 common Protorthopteron-Protoblattid stem and the Megasecop- 

 tera, and their line of descent either merged with that of the 

 Protorthopteron-Protoblattid stem and the Megasecoptera, or 

 paralleled them extremely closely, as they all approached their 

 common origin in an ancestral group resembling the Palaeodicty- 

 optera in many respects. The interrelationships of the primitive 

 forms grouped about the base of the lines of descent of the 

 Homoptera and the Neuropteroid insects is shown in the ap- 

 pended diagram (Text figure 1) in which the lines of descent in 



HEMIPTERA 



HADENTOMOIDA 



PROTORTHOPTERA- 

 PROTOBLATTIDA 



PALAEODICTYOPTERA 



NEUROPTERA 



MEGASECOPTERA 



PROTOHEMIPTERA 

 PROTEPHEMERIDA 



LEPISMATIDAE 



Fig.l 



question are represented as though branching off in different 

 directions, since this method apparently is more in accord with 

 the facts of a complicated interrelationship between these 

 groups of insects than is the case when one attempts to represent 

 their lines of descent by means of a dichotymously branching 

 tree. 



Having repeatedly stated that no living forms can be derived 

 from other living forms (see footnote to page 148 of the American 

 Naturalist, Vol. LIII, 1919, etc.) and since this fact is so widely 

 accepted as to be more of the nature of a truism, it hardly seemed 

 necessary to waste energy and space by repeating this utterly 

 obvious fact every time a living insect was compared with a. 



