THE HYPODERMIS 



679 



layer spreads from the place of their insertion, the layer con- 

 sisting of numerous small cells whose origin we must refer to the 

 peripodal membrane. This layer continues to spread over the sur- 

 face of the pupal thorax, while at 

 the same time the area of the 

 larval hypodermis, consisting of 

 large cells, is seen to diminish. 

 Hence the thin edge of the 

 newly-formed hypodermis (Fig. 

 631, hi) slowly grows into the 

 space between the superficial 

 cuticula and the larval hypo- 

 dermis (Fig. 632, 7i), so that at 



,1 i ,-1 -i j i j r iu. 001. jjiagrmii 01 me loruisuoii ui me 



tlllS place the Old nypOuermiS imaginal hypodermis on the abdomen .of Muscidw : 



i j hi. imagiDal buds of the hypodermis : lh. larval 



Undergoing destruction eveiltu- hypodermis. -After Lang. 



ally lies 011 the inner side of the 



newly -formed epithelial layer (B). We therefore see from this that, 

 during the replacement of the old hypodermis by the new, the con- 

 tinuity of the superficial epithelium is never interrupted. Since the 

 edges of the two kinds of hypodermis overlap, the surface of the 

 body is nowhere bare of epithelium. The dissolution of the larval 



FIG. 681. Diagram of the formation of the 



FIG. 632. Section through the abdominal bud of the hypodermis of Musca: A, of the larva; 

 B and C, of the pupa ; /, larval hypodermis ; h', separated portion of the same attacked by phago- 

 cytes ; i, imaginal bud ; k, phagocytes with what are called cell-wrecks or fragments (so-called 

 granulated cells) ; k', phagocytes enclosing hypodermal nuclei ; m, mesoderm-germ of the imaginal 

 bud ; w, wandering cells. After Kowalevsky, from Korschelt and Heider. 



