THE SALMON FAMILY 1 89 



the egg is first shed, and attaches itself to the surface it touches 

 or falls upon, so that the egg remains suspended or anchored 

 by the flexible membrane. Ehrenbaum found however many 

 eggs quite free, having been evidently torn from their attachment, 

 and this seems to happen frequently in consequence of the force 

 of the tidal currents. In the Elbe the fine net used at the bottom 

 always brought up much rubbish, consisting of fragments of 

 water plants, and among this were the smelt eggs, some attached 

 to the fragments, some free. 



After fertilisation a considerable space is formed between the 

 enclosing membi-ane and the body of the egg. The shape is 

 round and the breadth of the enclosing membrane varies from 

 •9 to 1-3 mm. (about ^^uo to yf^r inch). The yolk is composed of 

 small globules, and contains several oil globules of different sizes. 

 The whole egg is fairly transparent, but less so than marine 

 buoyant eggs. 



The development is rather slow and took at a temperature'of 

 46° to 53° twenty-seven days. In the earlier part of the spawn- 

 ing season, from the end of March onwards, the water being 

 colder, the development would take longer. The newly hatched 

 larva is 5-5 to 6 mm. long (yVo i^ch or a little less). The mouth 

 is already open, but beneath the head ; the }-olk is much reduced, 

 and the oil globules all united into one which is situated near the 

 front end of the yolk sac. The primitive fin membrane is narrow, 

 the intestine ends near the end of the tail, far behind the yolk 

 sac as in the larvae of the herring family. The pigment is very 

 scanty, there is some in the eyes and specks on the yolk sac and 

 along the lower edge of the body. The whole larva is very 

 delicate and transparent. 



The larvae were kept alive for fifteen days after hatching in 

 an aquarium. On the sixth day by the growth of the lower 

 jaw the mouth had become terminal and the yolk was nearly all 

 gone ; but the fins had not begun to appear (Fig. 97). The larva 

 at this age was 6'3 mm. long ({ inch). The youngest larvae 

 captured in the river were taken on the 5th to 8th May, were 6 

 to 8 mm. long (the largest nearly ^ inchj, and had already begun 

 to feed on the minute Crustacea, called copepods, the usual food 

 of young fishes. The larvae were extremely abundant in the 

 estuary of the Elbe, a small net only 2 feet 8 inches across the 

 opening placed in the current for a quarter of an hour captured 



