50 THE SEAS 



developed ; those which deposit adhesive spawn on to 

 stones, sea weed or empty shells ; and those in which eggs 

 and developing young are attached to the body of the 

 parent. In the first division are the sea urchins, starfish, 

 brittlestars, many worms, barnacles and the bivalve 

 molluscs. Since the chances of destruction are excessively 

 great, the number of eggs shed is correspondingly large, a 

 striking example of which is supplied by one of the larger 

 American oysters, which is said to produce 100,000,000 

 eggs annually ! If a sea urchin or mussel be watched when 

 spawning, it will be seen to discharge a cloudy fluid which, 

 on microscopical examination, will be found to consist of 

 incredible numbers of eggs or sperm. Yet so great are the 

 dangers to which these unprotected young are exposed 

 that the race does no more than hold its own ! 



If search be made among the rocks during the spring, 

 many kinds of spawn will be found. Common on the 

 under side of rocks are the egg-capsules of the dog-whelk 

 (Plate 13), which look like grains of corn, and are attached 

 by short stalks, occurring in groups of fift}^ a hundred or 

 even more. Each consists of a tough case, containing a 

 number of developing embryos, amongst which there is the 

 keenest competition, the weaker being eaten by the 

 stronger, so that finally only the one or two strongest emerge. 

 The sea slugs provide the most diverse and ornamental 

 spawn, covering the rocks with ribbons of jelly, often 

 beautifully coloured, in which lie embedded the developing 

 eggs. The common sea lemons (Plate 17) lay their eggs 

 in a broad band of pure white, ahvays arranged in a triple 

 coil, some fifteen inches long and about one inch wide, the 

 margin being unusually wavy. Over half a million eggs 

 may be laid in a single ribbon, for the young hatch out at a 

 very early and unprotected stage. The spawn of other 

 sea slugs shows other pecuHarities, some consisting of spirals 



