302 THE DEVELOPMENT OE THE NYMPH. 



tlie small epiblastic cells of the disc itself take its place and 

 form the hody-wall of the nymph. 



Although neither Kowalevski [145] nor Van Rees [147] recog- 

 nised the differences between the larval hypodermis and the para- 

 derm which they regard as the larval hypoderm in the pupa stage, 

 Viallanes [27] says : ' The hypodermic cells have become thicker 

 than they were in the larva ; their contours are effaced, so that 

 it is not possible to limit the extent of adjacent cells. The 

 protoplasm is not only more abundant, but it has acquired a 

 property not exhibited in the larva — it stains readily with 

 carmine and haematoxylin. The nuclei are, moreover, pro- 

 foundly altered.' Though there are inaccuracies in his de- 

 scription, I quote it to show that the changed appearance of 

 the cells has been observed. These new cells are certainly not 



Dkscriptiox of Pi.atk XVIII. 



The Histolysis and Regeneration of the Alimentar)' Canal, and the Structure of the 



Imaginal Discs. 



Fig. I. — A transverse section through the chyle stomach of a pupa four days old ; 

 d c, degenerating larval epithelium; e c, embryonic epithelium developed from 

 the scattered histoblasts of Kowalevski ; ff, elongated fusiform ceils ; / /, para- 

 blastic layer consisting chiefly of amceboid cells ; ph, phagocytes feeding on the 

 larval epithelium. 



Fii;. 2. — A transverse section of the rudimentary mesenteron of the nymph, from a 

 pupa five days old : d f, degenerating larval epithelium ; e e, embryonic epithelium 

 of the chyle stomach ; ff, fat body ; /, intestine of the larva forming the so-called 

 corpus lutemi ; //, parablast forming the provisional wall of the new mesen- 

 teron. 



Fic. 3. — Leucocytes from th.e pupa on the fourth ila) . 



Fi<;. 4. — Hypodermis of the larva, from a pupa a few hours cdd, in an advanced stage 

 of degeneration. 



Flu. 5' — One of the imaginal discs of the abdomen from a pu la four days old : 

 cu, larval cuticle ; d, the disc ; //, the paraderm by which the larval hypodermis 

 is completely replaced. 



Fig. 6. — Large granule cells from a pupa five days old. 



Fig. 7. — The edge of one of the wing discs from a pupa four days old, showing its 

 relation to the cells of the paraderm and the amoeboid cells, phagocytes, by which 

 the latter is removed. 



Fig. 8. — The paraderm from one of the intersegmental abdominal folds : /, superficial 

 cells ; p', palisade-like cells ; cii, inner cuticular layer (basement membrane) ; 

 /, leucocytes. 



Fig. 9. — A mesothoracic leg disc from a pupa about thirty hours old: e, epiblast ; 

 at, mesoblast ; s, provisional capsule. 



Fig 10. — The edge of the wing disc from a pupa about thirty hours old : ep, epiblast ; 

 »t, mesoblast ; />, parablastic reticulum ; s, provisional capsule. 



