392 



the tracheal epithelium is clear. The tracheal intima does 

 not suffer any corresponding change. 



The destruction of those lateral stigmatic trunks which 

 do not persist in the adult wasp begins in the freshly formed 

 pupa. Here the cells lining the lateral stigmatic trunks 

 undergo cytoplasmic degeneration. This stage is easily recog- 

 nized on account of the great hypertrophy of the nucleoli, a 

 condition so characteristic of the worn-out larval cells of 

 Nasonia. In close connection with the disintegrating stig- 

 matic trunks leucocytes may occasionally be seen, actively 

 removing t\\e dehiis. Whether the remains of the cells 

 (nucleus and cell wall) disintegrate of their own accord, or 

 whether leucocytes remove them, I am not definitely able to 

 say; the appearance of preparations rather suggested the 

 latter. 



Composing the epithelium of the stigmatic trunks are two 

 kinds of cells. There are large, purely larval cells, and much 

 smaller imaginal cells; it is only the former that grow during 

 larval life, and degenerate at the end of it. The imaginal 

 cells are clearly seen in even the youngest larvae at the bases 

 of the trunks (fig. 93). It is from these "imaginal nests" 

 that the whole tracheal system of the imago becomes formed. 

 (See below.) 



The whole process of (disintegration of lateral spiracles 

 occurs in the early stages of pupal life, much later, therefore, 

 than that of the tracheae; the stigmatic trunks which dis- 

 appear in this manner are the second, the third, and the fifth 

 to ninth, only the stigmata of the pronotum and propodeum, 

 and the newly formed pair of the twelfth segment (see below) 

 being retained. 



The whole system of tracheoles also disappears; in the 

 living insect, however, in which the tracheoles are clearly seen 

 through the transparent cuticle, no discontinuity in the 

 general structure of the respiratory system is apparent. This 

 is due to the fact that the new tracheal system is forming as 

 .the old degenerates (cf. figs. 88, 91). In the sixteen -hour 

 pupa the tracheoles still appear quite normal, though greatly 

 hypertrophied. But shortly after this leucocytes begin to 

 accumulate round the finer tracheoles of the head cavity and 

 the process of histolysis commences. Sometimes the leucocytes 

 may be observed forsaking their free, life iiLJthe-blood-^ ream ; 

 attaching themselves to a branching~system of tracheoles they 

 begin to crawl over these, and eventually phagocytosis com- 

 mences (figs. 88, 90, 91). By the time the larva pupates (six 

 to eight hours later) the finer tracheoles of the head have dis- 

 appeared, and the larger ones are rapidly undergoing the 

 same fate. 



