GENERAL FACTS ABOUT S^A FISH 39 



fishes. Thus, the rowhound {Scyllium) deposits large horny 

 capsules, each containing an embryo rowhound, and moored 

 by tendril-like processes at the four corners to any convenient 

 anchorage of rock or weed. During this period the embryo 

 is undergoing development to the comparatively advanced 

 stage at which it breaks through the walls of its prison. 

 Even among bony fishes there is more than one way of 

 maintaining the supply of the species. The eggs of diiferent 

 groups of fishes behave diflferently. Broadly, they are 

 divided into eggs which float, like those of the plaice 

 {Pleuronectes), and eggs which sink, like those of the herring 

 (Clupea). The former are known as buoyant, or pelagic ; the 

 latter as demersal. While, however, the eggs of the plaice 

 float separately, those of the angler-fish {Lophius), also of the 

 buoyant kind, float in immense sheets, just as we see the 

 spawn of frogs floating on inland ponds. A similar distinction 

 is noted among demersal, or sinking, eggs, for whereas those 

 of the herring lie at the bottom in adhesive masses, clinging to 

 stones or other substances, those of its relative, the shad, lie 

 on the bottom of rivers separately. Both the bony and the 

 cartilaginous fishes, moreover, number some that bring forth 

 living young, known as " viviparous " fishes. Among the 

 cartilaginous we have already seen this habit in the tope. 

 Among the bony fishes of our seas, it is remarked in 

 the bergylt {Sehastes) and in one of the blennies (^Zoanes) — 

 fishes, be it noticed, of very different groups. Some of the 

 rays, too, are viviparous, but the majority, at least of the 

 smaller, commoner kinds, deposit large egg-cases or capsules, 

 not unlike those of the rowhound, but unprovided with 

 tendrils. Among the sharks, on the other hand, the vivi- 

 parous habit is far commoner, and only two sharks in our 

 seas [Scyllium) are ovo-viviparous. The late Matthias Dunn 

 suggested that the egg-cases of the rays, lacking the useful 

 anchoring tendrils, were provided in lieu thereof with a glue 

 which, being insoluble in sea-water, serves the same purpose. 



