PROC. ENT. SOC. WASH., VOL. 24, NO. 6, JUNE, 1922 153 



THE DERIVATION OF CERTAIN TYPES OF HEAD CAPSULE IN 

 INSECTS FROM CRUSTACEAN PROTOTYPES. 



Bv G. C. CRAMPTON, Ph. D., Massachusetts Agricultural College. 



The evolution of the mandibles (Journal N. Y. Erit. Soc., 

 Vol. 29, p. 63) and of the paragnaths or "superlinguae" of 

 insects (Psyche, Vol. 28, p. 84), and the derivation of the maxil- 

 lae (Proceedings Ent. Soc. Washington, Vol. 24, p. 65) as well 

 as the cerci (Ent. News, Vol. 32, p. 257) and other structures of 

 insects, from crustacean prototypes, have been discussed in a 

 series of articles dealing with each set of structures in detail. 

 To the evidence of relationship drawn from these sources, I 

 would add in the present paper, the further evidence of the 

 head capsule, in support of the contention that the Crustacea, 

 more nearly than any other known arthropods, represent the 

 types ancestral to insects. 



As this investigation has progressed, and the comparison of 

 the various features in insects and Crus acea has been extended 

 to include more and more structu es from different parts of the 

 body, each additional study has merely served to strengthen 

 and confirm the view that the Crustacea are the nearest known 

 representatives of the types ancestral to insects. Furthermore, 

 there is no possibility of being deceived by "convergent" 

 development 1 in this instance, since the remarkable resemblance, 

 both anatomical and embryological, present in so wide a series 

 of structures from such different parts of the body, and extend- 

 ing even to the minutest details, in the two groups of arthropods, 

 can be explained only as the result of consanguinity rather 

 than of convergence! I would therefore maintain that all of 

 the available evidence points unmistakably to a crustacean, 

 or at least a "crustaceoid," ancestry for insects, although the 

 Symphyla have also preserved many ancestral features from the 

 common crustaceoid stock from which both they and insects 

 were derived. 



There are several very primitive types of head capsule occur- 

 ring among the Apterygota and certain of the lower Pterygota; 

 and apparently some of these types were developed at a very 

 early stage of insectan evolution possibly at the time the first 

 insects were evolved. One of these types, such for example 

 as that found in Japyx and Campodea, apparently harks back 

 to a symphyloid origin, since it is remarkably similar to the 



'Since convergent development is supposedly the result of the effects of similar 

 environmental conditions, it is difficult to believe that the environment of a 

 marine crustacean (or even a littoral one) can have enough in common with the 

 environment of a terrestrial insect (in some cases mountain-dwelling ones) to- 

 produce the astoundingly close similarity one finds in the minutest structural 

 details in the two groups of arthropods! 



