A study of a scorpion cuticle: I. The structure and staining reactions of the fully formed cuticle of Buthus quinquestriatus (H. & E.)

The fully formed cuticle of the dorsal and ventral surfaces of the mesosoma of Buthus quinquestriatus is differentiated into hard sclerites and flexible intersegmental membranes. No transitional regions as represented by the intermediate sclerite of insects are recognized, so that each sclerite is sharply marked off, anteriorly as well as posteriorly, from the adjoining intersegmental membranes. The difference in hardness between these two contrasting areas is due to the formation in the outer region of each sclerite of an exocuticle, but its absence from the intersegmental membrane leaves the cuticle in the soft unmodified arthrodial membrane condition. The exocuticle is, however, double in Buthus, and only the inner zone has the same appearance and staining affinity as the amber-coloured exocuticle of insects. The outer zone, on the other hand, finds no counterpart in insects. It is chitinous and, although it has a lemon-yellow appearance, it is readily homologized with the hyaline exocuticle of other scorpions. In a similar manner the sclerite endocuticle shows two zones of different appearance and staining reactions. The outer zone has properties identical with those of the colourless exocuticle of insects but is not to be regarded as its homologue. It is of a post-exuvial origin as is the underlying zone, and in the early instars both zones stain similarly, An epicuticle of the same basic structure as that of insects is present over the dorsal and the ventral surfaces of the cuticle. The function of the dermal glands is discussed in relation to the formation of certain of the epicuticular layers, and the form of the pore canals in different regions of the cuticle, together with the nature of their contents is described. In conclusion, it is suggested that in spite of certain points of similarity with the cuticle of insects, the scorpion cuticle resembles that of spiders more closely than has been hitherto recognized.