of the Fishery Board for Scotland, 125 
V.—ZONES OF GROWTH IN THE SKELETAL STRUCTURES 
OF GADIDA AND PLEURONECTIDA, By J. T. Cunnine- 
Ham, M.A., F.Z.S, (Plates VII-IX.) 
Previous In VESTIGATIONS. 
The primary object of Reibisch’s investigations was to ascertain what 
relations existed between the number of eggs produced by a plaice and its 
size or age, whether if the number of eggs varied, it depended on the size 
or on the age of the fish or on both. In describing his method of enume- 
rating the eggs to be shed in the following spawning season, Reibisch 
shows that he was not acquainted with my own paper on the develop- 
ment of the ovarian egg in Teleostei in general and Pleuronectide in 
particular published in the Quarterly Journal of Microscopical Science in 
1897. For he explains the opacity of the larger eggs in the ovary in 
August as due to oil-drops—“durch die Aufnahme einer grossen Zahl 
kleiner fett trépfchen zu erkliiren”—whereas I have shown that in 
Pleuronectes ova there are no oil-drops, but only yolk granules, while in 
the developing eggs of sole, mackerel, &c., both yolk granules and oil- 
drops are present and are easily distinguished from one another, 
Reibisch found great variations in the number of ripening eggs in 
plaice, and these numbers could not be brought into correspondence with 
either the weight or the length of the fish. He then found that the 
various numbers formed three principal groups, between which few or no 
numbers were found: thus there were large numbers of fish with eggs 
from 50,000 to 170,000, or from 220,000 to 270,000, but searcely any 
fish whose number of eggs lay between 170,000 and 220,000. It seemed 
therefore probable that the groups of numbers corresponded to different 
ages, and Reibisch sought for a method of ascertaining the age of the fish. 
He rejects entirely the markings of the scales as indications of the age 
in the plaice, stating that the lamination of the scale can be used for the 
purpose in view in the carp, but that this is impossible in the case of the 
plaice. The reasons he gives are that the presence of an annual lami- 
nation (Jahresschichtung) is scarcely to be demonstrated in the simple 
cycloid scales of the plaice, and further, that in almost all regions of the 
latter there occurs a transformation of the cycloid to the ctenoid form. 
But he seems to have misunderstood Hoffbauer’s work on the carp, for’ 
that author deduces the age, not from the lamellz, if such exist, but from 
the varying distance between the concentric lines of the scale, and these 
also occur in the scales of plaice. I have shown by my observations, 
described below, that the distinction of the growth of successive years in 
the scales of the plaice, from the different intervals between the concentric 
lines, is not impossible, The remarks of Reibisch concerning the 
transformation of the scales into the ctenoid form in the plaice refers 
to the Baltic variety on which he worked, in which spinules on the scales . 
are strongly developed, especially in adult males. But this does not affect 
the anterior embedded part of the scale, and I have not noticed spinules 
on the scales I have examined. The spinules are developed in adult males 
in the North Sea, but they are usually confined to limited portions of the 
I 
