The Development uf tlie Whigs of a Caddis-fly Platyphylax designatus Walk. 583 



first indication of this change being seen in a slight indentation along 

 its inner surface (Fig. 12). Up to the time that this last change takes 

 place a large majority of specimens show a great regularity of the 

 disk in its position within the peripodial cavity (Figs, 9A, 10^ and IIA) 

 and it is seen to face directly out towards the surface of the thorax 

 and the peripodial pore. With the beginning of evagination this re- 

 gularity ceases and the apex of the disk, outer surface, becomes more 

 acute and gradually changes to assume a more ventrally directed 

 Position; this is more marked in some transverse sections of the disk 

 than in others. At this stage there are naturally a number of variations 

 and irregularities some of which have been shown in text figure III; 

 in whatever way the evagination of the different specimens may differ 

 the apex of the rudiment always has a ventral inclination. 



Text figure III. 



Sections of four wiug rudiinents, from transverse sections of the larvae, to show variations aud 



irregularities at stages during early evagination. Dorsal above. x 280. 



As evagination continues the size of the rudiment increases, its 

 wall becomes thicker and the cells in this wall are longer and narrower 

 than they were in the early stages. The apex of the disk pushes well 

 out towards the external wall of the peripodial cavity and becomes 

 more ventrally inclined, the peripodial pore lengthens with the growth 

 of the rudiment being only in part seen from surface view (Fig. 14 Pp) 

 and the peripodial cavity becomes more elongated and in transverse 

 section the two arms of the crescent (it having in these sections a cres- 

 centic shape) elongate and reach up on either side of the rudiment 

 (Text figure IV). In the pocket the entire rudiment occupies a ventral 

 Position (Fig. 13 A) and the adjacent fat body, now much larger, is 

 seen to occupy the sanie relative position as in the earliest and sub- 

 sequent stages. The absence of setae on the area of the wing rudiment 

 is also the same and the darkened cuticula is still seen to cover the 

 underlying rudiment. 



38* 



