OBSERVATIONS ON COLEOPTERA. 



"83 



and softened by the dissolving action which is evidently going on. 

 As far as my experience goes this solution of the cuticula varies 

 greatly in different preparations, being almost but never entirely 

 absent in some and exceedingly active in others. I have not 



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FIG. 6. L. decimlineata. Section of pronotum in early part of the period of 

 ecdysis showing greatly drawn out hypodermal cells and almost entirely dissolved 

 secondary cuticula. Fragments of cuticula are floating in the exuvial fluid (C 2 ). 



determined absolutely what brings about this dissolution of the 

 secondary cuticula, but it is probably due to enzyme action. 

 Attempts have been made to isolate these enzymes but thus far 

 without any marked success. I do find, however, in the hypo- 

 dermal cells in the late part of the period of differentiation and the 

 early part of the period of preparation, granules which react and 

 stain exactly like zymogen granules and which are derived from 

 the nucleus by chromatolosis and which disappear after the action 

 of dissolution of the old cuticula has begun. These may not, 

 however, have anything to do with the disintegration of the old 

 cuticula. It is clear, however, that the action upon the cuticula 

 is chemical as there is not the slightest indication of phagocytes 

 or other organic elements being present. The most logical sup- 

 position is that the hypodermal cells secrete a substance that 

 dissolves the old secondary cuticula and thus thins and softens 

 the integument as well as supplying a considerable part of the 

 exuvial fluid, thereby greatly facilitating ecdysis. 



