30 



PSYCHE. 



existed in some previous phyletic 

 stage, paired rows of external, seg- 

 mental organs running down the back 

 of the insect from one end to the 

 other, just as the legs at one phyletic 

 period extended the entire length of the 

 ventral surface, and still do in the very 

 lowest insects, and further, that on the 

 thorax these organs developed finally, in 

 the evolution of insects, into wings. 

 Tracheal gills might represent such or- 

 gans. And the fact that the dorsal 

 prothoracic discs in Musca and the 

 nematocera develop into the pufjal 

 spiracles lends great weight to this 

 notion as these, like the tracheal gills, 

 are respirator}' organs. The v\ell 

 known theory of Gegenbaur and Lub- 

 bock, tracing the origin of wings in 

 insects to tracheal gills, seems thus to 

 obtain a new support. 



Another matter which seems worth 

 mentioning is that in diflerent holomet- 

 abolic insects, the extremities or the 

 thoracic and abdominal imaginal discs 

 (when such are present) may appear at 

 very diflerent times in the ontogeny. 

 In some insects these appear earl}', and 

 in some late, in the embryonic develop- 

 ment, in some early, and in some 



DIAPHEROMERA FEMORATA. 



I FIND among my notes the following ob- 

 servations on this insect in captivity. 



The general color of the female is brown, 

 marked by streaks and dots of a ligliter 

 brown or shaded darker at the sides of the 

 body and at each joint. The face is orange, 

 the antennae and palpi brown. Tlie legs 

 have a greyish green tinge and are lighter 



late, in the larval development. F'or 

 instance, in the lower orders of 

 holometabolic insects, as in those having 

 incomplete metamorphosis, the anlagen 

 of the extremities appear verv early in 

 the embryo. In Melophagirs the tho- 

 racic discs, homologous organs, appear 

 rather late in the embryo, wiiile the 

 abdominal discs appear probablj- early 

 in the larval period. In Corethra the 

 imaginal discs, also homologous to 

 extremities, delay their appearance un- 

 til just before pupation. Thus the 

 epigenetic period in insects, when new 

 organs are forming, does not end with 

 the birth of the larva from the ^^^, but 

 extends over the larval and even over 

 the pupal period. The embryonic 

 development of the insect really does not 

 end luitil the imago bursts from the 

 pupaiiinii. the embryonic, larval, and 

 pupal peiiods being essentially identical. 

 The principal significance of the pupal 

 period and the metamorjjhosis is that 

 it is the time when the larval characters 

 which were adopted tor use during a 

 period of free life in the midst of the 

 development, and whicii would be 

 valueless to the imago, are corrected 

 or abandoned. 



than the body, but darker at the ends of the 

 joints. The fore legs are always different in 

 color from the others being brown above and 

 dull yellow below and when stretched for- 

 ward beside the appressed antennae (which 

 just surpass them), as is always the case 

 at rest, they make the insect appear a third 

 longer tlian it is. They eat the edge of a 

 leaf, usually straddling it with their legs and 

 in an hour will devour a piece an inch long 



