200 



season an immense number of eggs must be present in tlie 

 seas round tlie spawning grounds, and this has been 

 approximately determined in various places. In a series 

 of remarkable researches on the quantitative estimation of 

 planktonic organisms Hensen* has made an approximate 

 determination of the floating fish eggs in various seas. 

 In the North Sea in 1895 he found during three voj^ages 

 an average number of 5()'8209 Plaice eggs per square 

 metre of the track of the vessel. From the known area of 

 the North Sea (547, 62-) millions of square metres) Hensen 

 determined the total number of Plaice eggs in that area to 

 be 31"117 billions. It is evident that this number can 

 onl}^ be approximately accurate, but there are reasons for 

 believing that it really underestimates the total quantity. 

 In much the same way, Williamsonf determined the total 

 quantity of Plaice eggs present in Loch Fyne during the 

 first eight months of 1898, and found a total number of 

 483 millions to be present in the loch during that time. 



The Egg is one of the largest of those belonging to 

 Pleuronectid fishes, and is on that account easily recog- 

 nised in plankton collections. Its transverse diameter 

 varies from 1'63 to 2'11 mm. It is enclosed in a fairly 

 tough capsule, the outer surface of which is finely 

 corrugated ; at one place, beneath which the germinal disc 

 forms, there is a minute opening in the capsule — the 

 microjjyle. There is no oil globule, and the contents of 

 the egg are of a glassy transparency and apparently 

 homogeneous. A small perivitelline space is present 

 between the yolk mass and the capsule. 



Before ripening the ovary of the Plaice contains only 

 opaque eggs considerably smaller than those extruded 



* Hensen u. Apstein — Wiss. IMeeresmitersuch., Kiel Commission, Bd. 2 

 (N. F.) Heft 2, p. 71, 1897. 



t 17th An. Ecport Scottish Fish. Bd., p. 79, 1898. 



