240 SALT-WATER FISHES 



are provided with an oil-globule ; those of the sole and its 

 four allies have a number of these globules ; and those of both 

 the plaice and halibut types have no oil-globule at all. As the 

 function of the oil-globule is obviously that of a swimming- 

 belt, to keep the egg afloat, it is not easy to understand why 

 the ova of fish so closely related should differ so materially in 

 this respect, and a satisfactory explanation has yet to be oflFered. 

 In addition to merely keeping the egg afloat, it should be 

 noticed that the presence of the oil-globule makes it float with 

 that end uppermost at which this contrivance is situated, 

 though in the eggs of the soles the small globules are so 

 generally distributed that this consideration is eliminated. 



For the most part, except when their spawning-time comes, 

 the flat-fish Hve in shallow water and on sandy, or muddy, 

 ground, two preferences that combine to put them at the 

 mercy of man and his trawls during the greater part of their 

 life. The only kinds that enjoy immunity from such constant 

 danger are the topknots, which live on rocky ground, 

 clinging to the smooth surface of the rocks with their fins in a 

 way that has already been described, and thereby escape the 

 sweeping trawl, which dare not work such rough ground. As 

 there is no regular line fishery for topknots, all statements as 

 to their geographical range, and particularly as to their scarcity 

 in any given locality, must clearly be accepted with all reserve. 



One curious habit all these flat-fish share which comes 

 perhaps within the cognisance of the angler rather than that of 

 the naturalist, and that is their behaviour when hooked. They 

 immediately curve the body, the white side being the concave ; 

 and this has the obvious result of immensely increasing the 

 resistance of the water, so that a comparatively small plaice or 

 dab feels enormously heavy when being hauled on fine tackle. 

 Whether, as seems not improbable, their instinct bids them 

 offer this increased resistance when they feel themselves being 

 hauled through the water, or whether their conduct is only the 

 outcome of muscular pain, can only be surmised. Another 



