FORMATION OF THF PRO.WMPH FROM THE LARVA. 301 



becomes spongy and scarcely stains at all with ha;matoxylin, 

 borax- or picrocarmine, and the vacuoles contain blood cor- 

 puscles and multinucleated phagocytes. The nuclei of the 

 epithelial cells are large and contain a large quantity of 

 clear substance in which a small reticulum of chromatin is 

 imbedded. This subsequently gives place to a mass of readily 

 stained material on one side of the nucleus. The nuclei 

 appear to be perforated by phagocytes. During these changes 

 the hypoderm becomes widely separated from the larval 

 cuticle ; and a very thin cuticular layer is developed on both 

 its outer and inner surfaces. 



Sections made from pupae an hour or two older show that 

 the whole pronymph is covered by a layer of cells, which 

 differ from those of the larval hypoderm. These new cells, my 

 paraderm, have far smaller nuclei, which are apparently solid. 

 The cells arc no longer spongy and vacuolated, and their 

 protoplasm, unlike that of the degenerating hypodermic cells, 

 stains intensely with haematoxylin and carmine. Like the 

 latter, they lie between the two cuticular laminae already men- 

 tioned. It is exceedingly difficult to trace the origin of the 

 paraderm. It either originates from the leucocytes developed 

 within the cells of the hypodermis, or the hypodermic cells 

 undergo a complete rejuvenescence. This later hypothesis 

 appears to me most improbable, and I regard it as almost 

 certain that the paraderm originates from leucocytes, and is a 

 true parablastic tissue, similar to that which Korotneff has 

 described as investing the yelk in the egg of Gryllotalpa before 

 the appearance of the epiblast. Indeed, I think some of my 

 sections (PI. XVIII., Fig. 4) show that the paraderm is formed 

 outside the degenerating hypoderm, and consists at first of 

 small but rapidly growing amoeboid cells. 



This parablastic layer is continuous with the pedicles of the 

 imaginal discs, as Van Rees described it. I only differ from 

 him in no longer regarding it as the hypoderm of the larva. It 

 is gradually absorbed after the epiblast of the disc becomes, as 

 it were, engrafted upon it ; for during the subsequent growth of 

 the disc the large parablastic cells disappear beneath it, so that 



