of the Fishery Board for Scotland. 



113 



example, the large opaque egg of the plaice with a diameter of 1*2 1mm. 

 has a volume of 0*9276 cubic millimetres, while the mature translucent 

 egg with a diameter of l*88mm. has a volume of 3*479 cubic millimetres, 

 nearly a four-fold increase. Another series of eggs of this species gave a 

 mean diameter of l*lmm. for the opaque, with a volume of 0*6969 cubic 

 millimetres; and of l*93mm. for the translucent, with a volume of 

 3*764 cubic millimetres. It has to be noted that the eggs, although 

 spherical, are not usually perfect spheres, and this is especially true of 

 the opaque eggs. The eggs of different females of the same species, and 

 even of the same female, also differ a little in dimensions. It is 

 therefore necessary to measure a considerable number to obtain a mean 

 diameter. But making all allowance for this variability and source of 

 error, the difference in the volume of the egg in the two stages is very 

 great. 



Fig. I. A. Opaque egg of plaice x 20 ; diameter, l*21mm. ; volume, 0*9276emm. ; 

 sp. gr., 1*070. B. Ripe egg of plaice x 20; diameter, l*88mm. ; volume, 3*479cmm. ; 

 sp. gr., 1*025. C. and D. Diagrams showing the volume of watery fluid that enters 

 the pelagic and demersal egg (herring) at maturation ; the shaded part represents 

 the yolk of the opaque stage. 



In the following Table I give the respective volumes of the large 

 opaque and the mature translucent pelagic eggs of a number of 

 Teleosteans, the calculations being partly founded on the mean of 

 measurements of the diameter made by Williamson* as well as on my 

 own observations. 



* On the variation in size of certain Pelagic Ova. Thirteenth Aimnal Report Fishery 

 Board for Scotl<mi, Part Hi., p; 271. 1895. 



