430 THE HERRING FAMILY. 



in the outer stations beyond the Isle of May, where the eggs 

 of the haddock and cod abound. 



The sprat appears to commence spawning about the end of 

 April and, in the areas indicated, its eggs are the commonest 

 form throughout May and June and into July. In the south 

 they spawn earlier, indeed Mr Cunningham 1 speaks of procuring 

 them in January at Plymouth. 



The egg is readily distinguished by a very thin capsule, a 

 beautiful translucency and a fine network of markings over the 

 whole surface of the yolk. It is usually about '04 inch in 

 diameter, Plate IV, fig. 19, though some, not round, have the 

 shorter diameter '039 in. ('94 to 1'2 mm.). The embryo, even 

 up to hatching, is perfectly colourless. The sprat is an 

 essentially oily fish but there is no trace of an oil-globule 

 in the egg, showing that there is no necessary connection 

 between these two features. 



The period of incubation is short, and the larva when 

 hatched, Plate XVIII, fig. 4, has no trace of pigment and 

 measures 3 - 07 mm. to 3'6 mm. There are peculiar paired 

 lateral sense-organs, and the vent is situated posteriorly, a 

 marked feature of the larval herring and sprat, and probably 

 a clupeoid characteristic. The marginal fin is slight and the 

 larva is not so elongated as that of the herring. The notochord 

 is unicolumnar. 



After 9 or 10 days of larval existence (Plate XVIII, fig. 5) 

 the supply of yolk has considerably diminished and the snout 

 protrudes in front of it. The mouth is not yet open but 

 the breast-fins are well-developed. The eye is slightly silvery 

 but otherwise there is no pigmentation. The sub-terminal 

 position of the vent is still diagnostic. At this stage the little 

 larvae in the Marine Laboratory died. They are pelagic and 

 very delicate. 



Ehrenbaum found that in a week the yolk was absorbed, 

 and the early post-larval conditions assumed at the length of 

 4'7 mm. (Plate XIX, fig. 7). Black pigment was well-developed 

 in the eyes, while two rows occurred along the alimentary canal, 



1 Journ. Mar. Biol. Assoc. I, (N. S.) p. 45. 



