Epicuticle of Blow-fly Larvæ

Abstract

IT is now clear that in many insects the epicuticle is the waterproofing layer of the cuticle. Although difficult to define morphologically¹, it often carries a wax layer, removable by abrasion or adsorption. Rhodnius² and Tenebrio³ undergo desiccation after removal of the wax layer by inert inorganic dusts; but blow-fly larvæ are unaffected⁴, suggesting a different constitution of the epicuticle. Indeed, the habits of blow-fly larvæ in liquefying the food in which they burrow suggests that the prime function of the epicuticle is other than the prevention of evaporation from the surface of the cuticle. Since the food is liquefied by the secretion on it of the digestive enzymes, it is desirable to discover whether or not a function of the epicuticle is to protect the underlying protein-containing endocuticle against digestion. The great chemical stability of the outer layer of the epicuticle is in agreement with such a view, for it is not dissolved by saturated potassium hydroxide solution heated to 160° C., or by cold concentrated hydrochloric or nitric acids. On boiling with concentrated nitric acid to which potassium chlorate has been added, however, it disrupts into oily droplets which stain with Sudan Black B. It therefore appears to be composed of the material termed cuticulin by Wigglesworth^1,5.