THE chitinous integument of many invertebrates consists not of chitin alone but also incorporates much structural protein. In the more highly sclerotinized arthropod shells, indeed, this may far exceed the true chitin. The methods frequently used for softening ‘chitin’ for histological purposes make use of this fact, and none of them actually alters the chitin itself, acting instead on the protein moiety of the integument. ‘Diaphanol’, for example, the most widely used agent for softening ‘chitin’, acts by breaking benzene rings in the aromatic amino-acid residues of the proteins1. Inevitably such an action is accompanied by extensive damage to the tissues of the specimen, for not only is the protein of the skeleton idigested but also the proteins of the tissues which we wish to examine. The use of diaphanol, or of other agents which digest the protein moiety of the chitinous integument, is therefore incompatible with precise histological or cytological investigation. If the integument consists mainly of structural protein, then we have no way out of the dilemma except to dissect the tissues free from all traces of the offending shell. If, however, as in the less-sclerotinized shells, it consists chiefly of true chitin, then it is possible to attack the chitin enzymically, leaving the tissues untouched.