LIFE HISTORIES 343 



gar-fish and the flying-fishes. In the smelt (Osmerus) which 

 belongs to the salmon family, and which spawns in estuaries, 

 the egg becomes attached to solid objects such as the gravel 

 bottom, or harbour piles and piers, by an outer adhesive mem- 

 brane. This membrane separates from the inner membrane 

 and becomes turned back, remaining attached to its central 

 part, much as the rind of an orange may be turned back without 

 being completely detached. Ehrenbaum, who studied the de- 

 velopment of the smelt in the Elbe, foui.d that large numbers 

 of the eggs became free and drifted to and fro with the tide 

 among the rubbish at the bottom of the water. In a few species 

 of fish the eggs are united together in a transparent gelatinous 

 mass which floats near the surface, as in the angler and in 

 Fierasfer. The sheet of spawn of the angler has been fre- 

 quently obtained off the south coast of England and off the 

 east coast of the United States ; it is usually from twenty-five 

 to thirty feet in length, and eighteen inches to three feet in 

 breadth. The spawn of Fierasfer forms little transparent cyl- 

 indrical masses two to three inches long. 



The spawning conditions of the Clupeidae are interesting 

 from the fact that the various species present a complete transi- 

 tion from the usual fresh-water condition to that which obtains 

 generally in marine fishes. The shads, Clupea alosa and C. finta 

 are anadromous, ascending rivers to spawn in the brackish or 

 nearly fresh water of estuaries. The eggs of these species are 

 free and separate, and simply lie loose at the bottom of the 

 water. The eggs of the herring are adhesive, and become firmly 

 attached to any fixed objects in the water they happen to fall 

 on. Herring shoals spawn at various distances from the shore, 

 and the few spawning grounds which are known from actual in- 

 vestigation are visited annually with great regularity. The eggs 

 adhere to one another and to other objects in small clumps or 

 layers. The ground where the spawn is deposited is usually 

 rough, consisting of coarse gravel, and at a depth of ten to 

 twenty fathoms, or in some cases more. In the Baltic herrings 

 ascend the rivers and in the Schlei the spawn has been found 

 attached to fresh-water plants. The sprat, on the other hand, 

 the pilchard (or sardine), and the anchovy all produce "pelagic 

 ova," that is to say ova which float separately in sea-water, and 

 undergo development in this condition. 



