The Early Post - moult Cuticle in Buthus

SINCE Krishnan (1953) reported the occurrence of —S—S— bonds in the cuticle of Palamnaeus swammerdami, a keen interest has been evinced in the cuticle of arachnids in general. Even earlier, Lafon (1943) noted the presence of over 2-85% of sulphur in the cuticle of Limulus and suggested that the cuticular proteins were similar in this respect to the keratinous type of proteins of the vertebrates. On another count, the cuticle of arachnids attracted the attention of workers in the field. Browning (1942) reported that what was considered to be the epicuticle in the spider, Tegenaria atrica,v/as only an optical artifact. Although later work on the same genus by Sewell (1955) showed the presence of an epicuticle, the homology of the arachnid epicuticle was once again a bone of contention; for Krishnan, Ramachandran, and Santanam (1955), studying the X-ray diffraction patterns of the epicuticle in Palamnaeus, observed the presence of chitin in this layer. Until then the epicuticle was considered to be a non-chitinous lipoprotein layer, distinct from a lamellated chitin/protein complex constituting a procuticle. Kennaugh (1959), investigating the cuticles of Pandinus imperator and Scorpiops hardwickii, reported that the epicuticle in these forms is free from chitin. What Krishnan described as the inner epicuticle corresponds to what Kennaugh called hyaline exocuticle. Shrivastava (1954) did not find any sulphur in the inter-moult cuticles of Palamnaeus bengalensis and Buthus. And again, on the basis of the amino-acid constitution of the cuticular proteins, Hughes (1959) suggested the possibility of the occurrence of quinone/sulphur links in an acarine. Thus the questions whether there was a chitin-free epicuticle and whether sulphur played a part in hardening the cuticle remained unsolved. Hence it was considered desirable to study the histochemistry of the newly exposed, soft, early post-moult cuticle of a scorpion.