6 MARKETABLE IJRTTISII MARINE FISHES chak 



simple. It ma)' be made of cheap muslin or expensive silk 

 bolting" cloth, but all that is required is a bag of any size made 

 of cloth of such texture that the water can pass through it, and 

 kept open at the mouth b}- a hoop of iron, brass, or wood. When 

 the net is hauled in, turned inside out, and its contents washed 

 into a jar of clean sea-water, living things of an extraordinary 

 variety and abundance are found. Among the material collected 

 b)- such a net Sars found a number of small, completely trans- 

 parent globules, which the microscope showed to be eggs of 

 some kind. These eggs became daily more abundant, until 

 about the end of March they were more numerous than any 

 other kind of thing in the sea-water. He was able to trace their 

 development, and found that a tender little fish was produced in 

 them, and at last hatched. He satisfied himself that these clear 

 globules were really the spawn of the cod in the following way : — 

 Numbers of cod were caught which were full of roe, and ripe,, 

 so that a little pressure caused the spawn to run out. He put 

 this spawn into clean sea-water. To quote his own words, 

 " This roe did not sink to the bottom, but floated on the water 

 like that which I had first observed. This peculiarity of the roe 

 of the cod-fish, to which no parallel is found in any other fish, 

 must be caused partly by the absence of the gluey matter which 

 in nearl}' all other fish holds the eggs together, partly by an un- 

 usually large quantity of fine oil contained in the egg, which makes 

 the specific weight of the roe a little less than that of the water. 

 Only when the foetus is dead, and the egg shrinks in consequence,, 

 does the roe sink to the bottom ; unless this is the case, it continues, 

 to float in the water during the whole period of its development ; 

 and even the young fish recently hatched floats about in a similar 

 manner, with its umbilical bag attached to it, which for some time 

 supplies it with food." There was no difference at all between 

 the spawn taken from the fish and that obtained from the sea. 

 It appears from Sars' report that in this first year he did not carry 

 out artificial fertilisation, but contented himself with comparing 

 the eggs in the sea with the unfertilised eggs obtained from the 

 female fish. The next year (1865) he continued his studies. He 

 kept numbers of the eggs in glass jars of sea-water till they were 

 hatched, and then kept the fry alive for more than two weeks. 

 The cod were very abundant this year, and in one region on a 

 calm da}- he found the sea covered with a thick layer of the 



