THE COD FAMILY 



301 



studied at Plymouth and St. Andrews. The chief pecuHarity is 

 the great length of the pelvic fins, which reach back behind the 

 vent and are of a deep black colour on their outer halves. 

 These fins develop very early and are seen in little fish only 6 

 or 7 mm. long (/g- or J-g- inch) when the rays in the dorsal and 

 ventral fins have only just developed. The peculiar front 

 dorsal is not visible. At this stage the skin and body are 

 somewhat transparent, not silvery, and there is black pigment 

 on the back. The breast-fins are short and rounded. In speci- 

 mens from f to I inch in length can be traced the gradual 

 development of the silvery livery in the skin, of the front 

 dorsal fin, and the gradual reduction of the long throat fins. 

 Fig. 138 represents a specimen a little more than | inch long. 

 Above I inch in length, up to i| inches the fish remains 



Fig. 138. — Young of the Three-Bearded Rockling in the surface-swimmint: 

 condition, a little more than 5- inch long. 



brilliantly silvery and swims at the surface of the sea, and the 

 barbels begin to appear on the snout. 



In calms during May and June, off Plymouth immense 

 numbers of these little fish have been seen from the deck of a 

 mackerel boat. It usually happens at the same time that the 

 surface of the sea is covered everywhere with great quantities 

 of minute round grains, which are living things of low organisa- 

 tion called Noctiluca. These are transparent when seen singly, 

 but are in places collected in vast numbers into a thick scum of 

 a salmon-pink colour, which floats in patches and streaks ; this 

 scum has a peculiar, not very pleasant, odour. The substance is 

 wrongly supposed by the fishermen to be the spawn of the 

 mackerel. This Noctiluca is one of the living things in the sea 

 which gives out light in the dark, and the sight from the bow of 

 a mackerel boat going slowly through the water before a gentle 



