Abstract
1. The ash amounts to only 0.365% of the dry weight of cleaned, water-washed cuticles of Sarcophaga (fly) larvae, to only 0.095% of cuticles of Limulus (Horseshoe crab). These values are considerably lower than ash values for whole insects or for cellular structures in general.
2. Elemental analyses show at least 25 elements in the ash of these cuticles. Ten are present in amounts > 1% of the ash. Magnesium is the predominant cation.
3. The percentage values for the elements do not agree well with the per cent composition of the solids of sea water or arthropod blood or calcified cuticles.
4. The cations are closely balanced by the anions. This implies that the ash components are largely present as salts which are either insoluble or sorbed.
5. Chitin carefully purified and washed in polyethylene vessels is ash-free.
6. The cuticulin sublayer of the epicuticle (thin surface layer, Fig. 3) leaves a relatively large amount of ash which is qualitatively different from that of the thick underlying procuticle. The iron of the cuticle is concentrated here.
7. The procuticle (Fig. 3) leaves relatively little ash. This ash residue shows a laminar organization similar to that of normal cuticle.
8. After sclerotization (hardening and darkening) the ash residue of the epicuticle seems unchanged but that of the procuticle is greatly reduced except in the tonofibrillae (muscle attachment points). Sclerotization, then, is accompanied not only by partial dehydration as reported by previous workers but also by extrusion of most of the ash components from the exocuticle.