Whence the Shadows? 



237 



In this rare photograph, a pair of Cat sharks (Scyliorhinus caniculus) are shown in 

 the act of mating at the Biological Institute, Helgoland, Germany. The male has 



wrapped itself around the female. Courtesy, German institute of Fisheries 



formed for each other sexually. Male claspers vary considerably in size 

 and shape. Males of some species have claspers equipped with hook-like 

 structures apparently used to aid in grasping the female. Females of these 

 species are protected by thick layers of skin. 



All Selachian young develop within the mother in ways that vary 

 among species. Some sharks are oviparous, laying unhatched eggs; others 

 are viviparous, producing live young nurtured in the womb; some are 

 ovoviviparous, forming eggs that are hatched within the mother, who 

 then brings forth her young alive. 



In oviparous sharks, the fertilized eggs pass down the two oviducts 

 to the shell gland where a capsule or envelope is formed around the eggs 

 containing a semi-fluid substance (similar to the "white" of a chicken 

 egg) that surrounds the eggs. 



The richly variegated capsules— oval-shaped, pear-shaped, spiraled; 

 amber, yellow, black, brown— are formed of a substance resembling 

 keratin, the same ingredient that imparts hardness to animals' claws, 

 hoofs, and horns. In sharks, the outer surface of the capsule is usually 

 smooth or finely ribbed. The four corners of the capsule are drawn out to 

 form long tendrils which coil themselves around rocks or other objects on 

 the sea bottom. Not only do these tendrils act as anchors for the egg 

 capsule, they also seem to aid in the delivery of the capsule from the 

 mother. The tendrils project from the mother and coil around some 



