200 
season an immense number of eggs must be present in the 
seas round the spawning grounds, and this has been 
approximately determined in various places. Im 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 voyages 
an average number of 56°8209 Plaice eggs per square 
metre of the track of the vessel. From the known area of 
the North Sea (547,625 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 
only be approximately accurate, but there are reasons for 
believing that it really underestimates the total quantity. 
In much the same way, Williamsont 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 
micropyle. ‘here 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. Meeresuntersuch., Kiel Commission, Bd. 2 
(N. F.) Heft 2, p. 71, 1897. 
+ 17th An. Report Scottish Fish. Bd., p. 79, 1898. 
