254 Shark and Company 



Skates are oviparous without known exception, and their oblong egg 

 capsules are essentially the same as the oviparous sharks' capsules. But, 

 instead of tendrils, the skate's capsules have stiff, pointed horns pro- 

 jecting from all four corners. The capsules are generally coated on one 

 side with a sticky substance. Small pieces of shells, stones, or seaweed 

 adhere to it and help to keep it on the bottom. Sometimes, too, the 

 horns imbed themselves in the muddy or sandy bottom which the skate 

 usually chooses for her hatchery. 



Half buried in the sheltering silt of the sea bottom, or snugly moored 

 to a staunch rock or other anchorage, the egg capsule becomes an in- 

 cubator for the embryo developing within it. (Raja binoculata some- 

 times has seven!) The capsule will be the embryo's home for a long 

 time— at least 4^2 months, sometimes as long as 15 months. The tough, 

 horny shell protects the embryo from predators, but, more important, 

 the capsule provides its charge with the stuff of life itself: oxygen. Either 

 by osmosis or by tiny perforations in the capsule, sea water enters and 

 leaves, bathing the embryo with oxygen and carrying off carbon dioxide. 

 Thus, in the early stages of incubation, the capsule acts as a natural sea 

 environment for the embryo. 



Nourishing albumen engulfs the embryo, which feeds upon it. The 

 embryo's diet also probably includes some chemical nutrients carried 

 in by the sea. In some species, a plug of albumen seals the slits in the 

 shell. After a while, the albumen is absorbed, thus unsealing the slits. 

 In other species, a delicate membrane temporarily seals the slits. When 

 the slits (located in the horns of the skate's capsules) open, a current of 

 water flows freely through the capsule. When its incubation is com- 

 pleted, the skate slips out of an incredibly narrow slit in the capsule and 

 begins its free life in the sea. 



Alany skates, including some that are common on the Atlantic, Gulf, 

 and Pacific Coasts, have electric organs in their tails. The output of these 

 organs is feeble, and there is no record of a fisherman ever having been 

 shocked by a skate. While the Electric rays (family Torpedinidae) can 

 produce a potent shock, the puzzling electric organ in the skate is differ- 

 ent from the Electric ray's. The skate's organ is linked by nerves to the 

 spinal nerves; the Electric ray's electric organ is linked to the cranial 

 nerves. 



Although much is known of the electrical organs found in the Tor- 

 pedinidae and other sea creatures with similar organs, little is known 

 of the skate's electrogenic ability. However, recent studies of 22 species 

 of skates in Japanese waters showed that every species had electrical tis- 

 sue in its tail. Dr. Reizo Ishiyama, who made the study, has raised the 

 possibility that all skates may eventually be found to have electrogenic 

 capabilities— though for what use, no one yet knows. 



