Vol. XXVlii] ENTOMOLOGICAL NEWS. 29" 



ment in the same specimen." Gerris niarginatus exhibits the 

 same gradation from apterous to macropterous, going from 

 one to the other by imperceptible degrees. Yet it is essentially 

 an alate species, since the bulk are fully winged and only a 

 small number totally apterous, with an indefinite proportion 

 of varying degrees of brachypterousness. In this it differs 

 from rcmigis and other species of the subgenus Aquarius, 

 which are in general totally apterous with a very small number 

 an occasional specimen here and there fully winged (ex- 

 cept conformis, always found fully winged, and alastor Bueno 

 MS., nearly always with rudimentary wings only). The most 

 complete study of pterygopolymorphism is Reuter's "Poly- 

 morphisme des Hemipteres 6 ." Here he covers the entire sub- 

 ject and hazards explanation based on selection. In Gerris 

 marginatus and in general in the family, I see a gradual trans- 

 formation to apterousness, through disuse, as exemplified by 

 our rcmigis and the European najas_, the fully winged being 

 the primitive form, adapted to an existence on the water from 

 an antecedent Reduvioid land bug, whose mobility depended 

 on these members. The stream species, being in general safe 

 from the consequences of droughts, are so independent of 

 wings for transportation that these organs are nearlv o-one in 

 most of them. The species inhabiting land-locked bodies of 

 water must, however, always have some means of travelling 

 if the water on which they live dries up, as so frequently hap- 

 pens with small ponds or water-holes. Hence wings still nor- 

 mally persist in these forms. 



Structure, progression, respiration, reproduction arc as 

 in G. rcmigis. Dufour (op. c., p. 199), states that in palmium 

 the digestive system is as in caiialimn, excepting the salivary 

 gland. 



Gerris marginatus, so far as known, has no egg parasites. 

 Adults and nymphs are sometimes found with larval mites at- 

 tached as in re 111! i/is, particularly about the head and thorax. 



Egg. The egg is cylindrical, truncate at one end and round- 



61875. Bull. Soc. Ent. Fr., pp. 225/36. 



