THE DEVELOPMENT OF THE NYMPH. 323 



head discs. Weisrnann says : ' The formation of the antennse 

 resembles that of the legs. First an oval furrow appears, which 

 has a considerable extent and encloses an ovoid projection. 

 The latter resembles the nucleus of the leg disc. Very soon 

 three concentric furrows appear within it, so that the ovoid 

 body is divided into three segments, the three rudimentary 

 antennal joints." And he adds : ' Even on the second day of 

 the pupa the antenna has scarcely any resemblance to the 

 developed organ.' 



In Plate IV. the appearance of the antenna is repre- 

 sented in an advanced stage of the resting larva, on which 

 Weismann relied for his conclusions. In a still younger larva, 

 however, from which Fig. 13 was constructed, the antennae are 

 well seen in sections, and bear an unmistakable resemblance 

 to the developed organs. The folds which surround the 

 antenna at a more advanced period, and mask its true charac- 

 ter, are developed from the part of the disc which becomes the 

 face and forehead, and not, as Weismann supposed, from the 

 antennal rudiment. These folds possibly form the two basal 

 joints of the antenna, which are well seen in some of my 

 sections on the second day of the pupa, when they are almost 

 as large as the third joint. 



In comparing the development of the antenna; with the legs, 

 Weismann was probably biased by the belief that these organs 

 are homologous with ventral appendages. The difference in 

 the development of the two structures is very marked. The 

 antennae are first mere ridges of the head disc, enclosing the 

 rudiments of the antennal nerves, and never become biramous 

 at any stage of their evolution. Nor are they ever, enclosed in 

 separate provisional capsules distinct from those enclosing the 

 optic discs. 



Changes in the Disposition of the Eye Discs. — The eye discs in 

 the resting larva (Fig. 13) lie in diverticula of the cephalic in- 

 volution. Their corneal (outer) surfaces look outwards and 

 forwards, and are covered by a provisional membrane. In the 

 next stage the provisional sacs have become part of the cephalic 

 involution, and the eye discs are thickened and plicated (PI. IV.) 



