DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 669 



Pelagic Ova. 



General Remarks. — The pelagic nature of the ova of so large a number of valuable 

 food-fishes removes them altogether from many of the vicissitudes which befall demersal 

 eggs. Their transparent glassy nature, minute size, and enormous abundance, sufficiently 

 provide for their safety and the increase of the species. Pelagic ova are by no means 

 common in the stomachs of fishes, while ova deposited on the bottom {e.g., those of 

 Cyclopterus, Cottus, and Clupea harengus) are eaten by many fishes with great avidity, 

 yet the numbers of one of these at least are, so far as can be made out, by no means 

 seriously affected. How much more surely, then, is the multiplication of those with 

 pelagic ova provided for ? As a rule, they are deep enough to escape the vicissitudes of 

 the immediate surface, and in our country are seldom stranded on the beach in numbers 

 sufficient to attract attention.* The larvae which escape from them are also minute and 

 translucent, and thus are less prone to attract the notice of predatory marine forms ; more- 

 over, they soon become very active, while their purely pelagic life gives them a vast area 

 for their safe development. 



The contrast between such types and the condition, for instance, in Cottus, is marked. 

 In the latter the ova are deposited between tide-marks in masses, and are often devoured 

 by other fishes, and it may be by predatory birds and mollusks. The comparatively large 

 young are conspicuous objects, and can only escape by keeping within reach of tangles 

 and other sea-weeds, a constant reduction of their numbers taking place, notwithstanding 

 their defensive armature, during the somewhat slow growth to the adult condition. It is 

 possible, indeed, that though the egg-capsules in Cottus are much denser, and the embryos 

 larger and more highly developed than in the cod, a much greater number of the latter 

 proportionally reach maturity than in the case of the former. 



On the eastern shores pelagic ova begin to appear at the end of February, though 

 there is no reason why some should not be found earlier, as Dr J. Murray tells us they 

 are on the west coast (Clyde district), and a kind of succession of those of different species 

 occurs throughout the spring, summer, and autumn. Amongst the earliest are the ova 

 of the plaice, Motella, and the large egg with the spacious peri vitelline space, the larval 

 form issuing from which is described subsequently. Those of the Gadoids, such as the cod, 

 haddock, and whiting, next appear, and also those of the flounder and dab, while towards 

 the end of the month the eggs of the gurnard are also captured. April is characterised 

 by the abundance of pelagic ova, the maximum perhaps being attained towards the latter 

 part of the month, when the ova of the sprat t and other forms swell the list. As an 



at times noticed the little transparent globular bodies in the water; but it never occurred to them that they were the 

 eggs of any fish. They may be found at the surface in common with the eggs of pollack, haddock, and probably other 

 species of the cod family, when the sea is smooth, but when the water becomes rough they are carried to a depth of 

 several fathoms by the current, though the tendency is to remain near the surface " (No. 8, p. 715). 



* G. 0. Sars found, however, that they were so at Lofoten. 



t Hensen first noticed the pelagic ova of the sprat, and his observation has been corroborated by J. T. Cunning- 

 ham and ourselves. Other Clupeoids, as shown by Raffaele, also have pelagic eggs. 



