HISTOCHEMICAL STUDIES ON THE NATURE AND FORMATION OF EGG CAPSULES OF THE SHARK CHILOSCYLLIUM GRISEUM

¹ Department of Zoology, University of Madras, India

1. The egg capsules of Chiloscyllium griseum, when first formed in the oviducts, are soft and white and gradually turn light brown to deep reddish brown before being ejected into the sea.

2. Light brown capsule walls show in section an outer and an inner narrow layer apparently homogeneous and yellowish in color while a wide central region is laminated and uncolored. This layer stains blue with Mallory, indicates the presence of a simple protein positive to biuret test and lacks chemical resistance. The outer and inner layers stain red with Mallory and contain a protein which is positive to Millon and xanthoproteic tests indicative of phenolic groups. In deeply colored walls the central laminated layer shows staining and histochemical reactions similar to those of the outer layer.

3. Evidence has been presented indicating that the above changes may be due to the tanning of a basal protein involving a phenol oxidase resident in the capsule wall.

4. The constituents of the tanning system are derived from the secretions of the cells of the nidamental gland. The tanning of the egg capsule protein does not appear to involve free diphenols so that some form of auto-quinone tanning seems to occur.

5. The tanned protein of the egg capsule is unlike the sclerotin of the insect cuticle, but recalls in its staining and histochemical reactions the protein precursor of tanning impregnating the presumptive exocuticle of insects like Periploneta.

6. The nature of the egg capsule protein has been investigated using microchemical and chromatographic methods. From the results obtained it is suggested that it is allied to the collagen group of proteins.

7. The results are discussed.