128 TEXT-BOOK OF ENTOMOLOGY 



crumple, thus forming a cavity. While the larva is transforming 

 into the pupa, the sheath or peripodal membranes of the rudimentary 

 wings are drawn back, the blood presses in, and thus the wings are 

 everted out of the peripodal cavities. 



Due credit, however, should be given to Herold, as the pioneer in these studies, 

 who first described in his excellent work on the development of Pieris brassicce 

 (1815) the wing-genus in the caterpillar after the third moult. This discovery 

 has been overlooked by recent writers, with the exception of Gonin, whose 

 statement of Herold' s views we have verified. Herold states that the germs of 

 the wings appear on the inside of the second and third thoracic segments, and 

 are recognized by their attachment to the "protoplasmic network" (xfhli-im- 

 netz), which we take to be the hypodermis, the net-like appearance of this 

 structure being due to the cell-walls of the elements of the hypodermal mem- 

 brane. These germs are, says Herold, also distinguished from the flakes of the 

 fat-body by their regular symmetrical form. Fine trachese are attached to the 

 wing-germs, in the same way as to the flakes of the fat-body. It thus appears 

 that Herold in a vague way attributes the origin of these wing-germs, and also 

 the germs of the leg, to the hypodermis, since his schleimnetz is the membrane 

 which builds up the new skin. Herold also studied the later development of 

 the wings, and discovered the mode of origin of the veins, and in a vague way 

 traced the origin of the scales and hairs of the body, as well as that of the colors 

 of the butterfly. 



Herold also says that as the caterpillar grows larger, and also the wing-germs, 

 "the larval skin in the region under which they lie hidden is spotted and 

 swollen," and he adds in a footnote: "This is the case with all smooth cater- 

 pillai's marked with bright colors. In dark and hairy caterpillars the swelling 

 of the skin through the growth of the underlying wing-germs is less distinct or 

 not visible at all" (pp. 29, 30). 



It should be added that Malpighi, Swammerdam, and also Re'aumur had de- 

 tected the rudiments of the wings in the caterpillar just before pupation under 

 the old larval skin. Lyonet (1760) also describes and figures the four wing- 

 germs situated in the second and third thoracic segments, but was uncertain as 

 to their nature. Each of these masses, he says, is "situated in the fatty body 

 without being united to it, and is attached to the skin in a deep fold which it 

 makes there." He could throw no certain light on their nature, but says : " their 

 number and situation leads to the supposition that they may be the rudiments 

 of the wings of the moth" (pp. 449, 450). 



During the transformation into the pupa the imaginal buds unite 

 and grow out or extend along their edges, while the enveloping mem- 

 brane disappears. The rudimentary wings are now like little sacs, 

 and soon show a fusion of the two wing-membranes or laminae witli 

 the veins, while the trachese disappear, the places occupied by the 

 tracheae becoming the veins. " Very early, as soon as the scales are 

 indicated, begin in a very peculiar way the fusion of the wing- 

 laminae. There occur openings in the hypodermis into which the 

 cells extend longitudinally and then laterally give way to each other. 

 Hence no complete opening is found, but the epithelium appears 

 by sections through a straight line sharply bordered along the wing- 



