NO 1310. NORTH AMERICAN THYS A NOPTERA— HINDS. 213 



GENERAL (lONSIDERATK )NS. 



As has been shown in Jordan's conchision in regard to the S3"stem- 

 atic position of this oroup (see p. 82), Thysanoptora have branched off 

 from the line of the Orthoptera-Hemiptera and res(nnblethe Honiop- 

 tera more closely than they do any other t^rou}). 



Startin<;' with a oiven form which we may call Prothysanopteron, 1 

 believe that changes in the degre(> of d(>velopmcnt of any of its organs 

 must be correlated Avith changes in its habits and environment. What 

 was Prothysanopteron like^ Judging from its line of phyllogeny, it 

 must certainly have been an active running and flying insect, having 

 elongated mouthparts which were pro])aV)ly ])ecoming suctorial in 

 function and ])earing near the other extremity of the body a saw-like 

 ovipositor. Having these organs which would be concerned in the 

 chief relations of its life to its environment — nutrition, locomotion, 

 and reproduction — what can we infer as to the habits of that primi- 

 tive insects It fed externally upon the juicy parts of plants, proljabl}-^ 

 puncturing them with its elongated mouthparts and sucking up the 

 exuding juices. It flew^ from flower to flower or tree and ran about 

 actively thereupon. In the tissue of its food plants it deposited its 

 eggs, cutting the necessary slits for them with its saw-like ovipositor. 

 Its legs, used chiefly in running or crawling, would present few. if 

 any, modifications, while its wings, though surely slender, were prob- 

 ably broad as compared with those found in the order to-daj^ and the 

 hairs which happened to stand along their edges had begun to elongate 

 so as to compensate, in some degree, for the narrowness of the juem- 

 branes. With sucih an insect and such habits as this hypothesis sug- 

 gests, if we can name reasona))le changes in habits which, acting in 

 accordance with the laws of Nature as we know them to be acting- 

 to-day, will produce the various forms of insects which we now include 

 in this order, we feel that our hypothesis can be as well sustained as 

 any such hj'pothesis with reference to primitive forms is capable of 

 being. 



If some of the descendants of our external-feeding Prothysanopteron 

 in their struggle for existence should, in the course of numerous gen- 

 erations, acquire a habit of feeding in some well-protected part of the 

 plant, e. g., inside the closely rolled central leaves of Jl(ccaJiJ<(ii(rntosa^ 

 where they would be comparativeh" safe from the attacks of their ene- 

 mies (a change of habit easily produced by natural selection), then, 

 this environment being favorable, they w^ould no longer find as fre- 

 quent or as urgent use for their wings and legs as liad their ancestors, 

 and they would be favored by remaining in a very restricted place. 

 As a result, wings would degenerate from disuse, and the movements 

 of the insects upon their feet would become slower, ^^'ings might, 

 and ]:)robably would, be a distinct disadvantage in such a restricted 

 ha))itat, so that many influences would tend toward their reduction, 



