521 



Fig. 84. Metamorphosing anterior transverse tracheal trunk, 

 eight hours after defaeeation (xoOO). Note the tracheoblasts 

 advancing from the sides, beneath the degenerate epithelium, 

 which has not yet begun to disappear. 



Fig. 85. Part of the sam.e vessel, eight hours later. A 

 remnant of the larval epithelium is still seen. Xote the larval 

 spiral intim.a within the developing imaginal intima. Note also 

 the "ridging" of the epithelial cells (x500). 



Fig. 86. Metamorphosing abdominal longitudinal tracheal 

 trunk, from the defaecating larva (xlOOO). Note the imaginal 

 cells advancing upon the degenerate larval cells, which are partly- 

 disintegrating, partly still intact. Leucocytes are present, and 

 three are attacking a tracheole. A large imagin>al tracheole is 

 beginning to grow out from the regenerated epithelium. 



Fig. 87. Central nuclear region of the great tracheal cells 

 iindergoing phagocytic histolysis — fresh pupa (xlOOO) (cf. fig. 81). 



Fig. 88. From the large regenerated tracheal vessel (i.tr.) a 

 multicellular tracheal vessel is extending (loicnu-ards into the 

 wing. Beside it a dead larval tracheole (trl.) is being over- 

 whelmed by leucocytes. The figure also shows disintegrating 

 salivary gland tissue, being attacked by leucocj'tes. Some of the 

 gland tissue has been ruptured by the growing tracheal vessel. 

 (Figure drawn inverted; xSOO'.) From four-hour pupa. 



Fig. 89. Cell proliferation of prothoracic stigmatic trunk 

 (x52o). Defaecating larva. 



. Plate XXIII. 



Fig. 90. Larval tracheoles undergoing phagocytosis ( x 1000) 

 — four-hour pupa. 



Fig. 91. From the regenerated neck tracheal vessel (i.tr.) 

 a very large tracheal trunk has grown downwards and teraiin- 

 ated near the mouth. A larval tracheole (trl.) is degenerating, 

 without intervention bj' phagocytes. From the base of the head 

 a column of myoblasts-r-developing into the head musculature — 

 has grown up supporting itself upon the dead tracheole. The 

 break of the column is due to its bending out of the plane of 

 section. The figure may be regarded as continuous with fig. 88 

 on its left (four-hour pupa; xoOO). 



Fig. 92. Longitudinal section of integument of defaecating 

 larva, in region of an abdominal stigmatic trunk, which will not 

 be reformed in the pupa. Notice the hypertrophied larval cells 

 and the proliferating embryonic cells, especially at base of trunk. 

 A fat-bodv and a group of imaginal oenocvtes are also seen 

 (x800). 



Fig. 93. Stigmatic trunk of larva in first instar showing 

 imaginal "nesf (i.t.c). 



Fig. 94. Developing dorso-lateral air sac — fresh pupa 

 < XlOOO). 



Fig. 95. Portion of wall of a mature air sac (four and a half 

 day pupa). Notice that a tracheole has grown out from it. Four 

 nuclei, and ''spirals" are also seen (xlOOO). 



Fig. 96. A cell of the fat-body from thorax, four and a half 

 clay pupa. Note the disappearance of storage products (x800). 



Fig. 97. The same, a little later, being attacked bv three 

 leucocytes (xlOOO). 



Fig. 98. A fat cell, drawn out and compressed between the 

 great thoracic muscles ; note diminution in quantity of storage 

 material (xlOOO). 



