of the Fishery Board for Scotland. 131 
bodies composed of elongated cells: these are sense-organs, which in the 
cod are freely distributed over the surface of the skin, in addition to the 
special organs of the lateral line. The derma below the epidermis 
consists of fine fibres having a horizontal direction, with numerous nuclei, 
and in this occur the scale-pockets containing sections of the scales. Of 
these, three layers at three different levels are seen in most sections, in 
consequence of the fact that the scales are imbricated, and overlap one 
another, so that portions of three different rows of scales are cut by one 
section vertical to the surface. The relations of the sclerites to the lower 
homogeneous portion of the scale are shown in the figure, but the cellular 
investment of the scale is not represented, as it is not sufficiently distinct 
under a low power. 
The ridges on the scales are seen to be farther apart in some regions, 
more closely crowded in others, so that zones may be distinguished. In 
other words, the sclerites formed at some periods of the growth of the 
scale are narrower than at others, so that their ridges are closer together. 
There is good reason for believing that the narrower sclerites are formed 
in winter, when the temperature is low. In the cod I find that the end 
of a year’s growth is usually indicated by one or two markedly narrow 
rings, while the gradual narrowing of the sclerites as this boundary is 
approached, though it can be made out, is not at first obvious. In these 
points my observations agree generally with the descriptions and cenclu- 
sions of Mr. J. Stuart Thompson, who, however, though he studied 
several species of Gadide, did not investigate the cod. In larger and 
older specimens several annual zones can be distinguished, each termi- 
nated by a winter zone, between which and the summer growth there is 
often a distinct contrast. The distinction however, is not so obvious as 
in the earlier or inner zones, and it would be very difficult, from the scales 
alone, to form a decided conclusion as to the age of a cod. 
Dr. Heincke has pointed out, in his paper in the Report of the Inter- 
national Investigations, shortly to be published, that lines of growth are 
more or less distinctly visible in various bones of fishes, while the lines 
and zones of the otolith have previously been investigated in the plaice 
and herring. In the cod I have examined the bones of the pectoral 
girdle, of the operculum, of the skull, and of the vertebral column. 
The pectoral girdle differs from that of the plaice in several particulars. 
“The cleithrum (the large superficial bone behind the branchial cavity, 
formerly known as clavicle) is thinner, and only the scapula is directly 
attached to the posterior and inner aspect of the cleithrum. There is a 
long and strong post clavicle. The cleithrum is ossified, but the scapula 
and coracoid consist of calcified cartilage. There is no scapular foramen. 
There are four distinct and partially ossified fin-supports, instead of one 
cartilage, as in the plaice. The form of the parts is shown in fig. 20, pl. ix. 
I could not satisfactorily make out annual zones in any of these structures, 
On the thin transparent part of the cleithrum there are sometimes visible 
some lines parallel to the edge, but they are very indistinct. Also in the 
coracoid there are slightly opaque lines parallel to the edge, but still less 
distinct, and no definite conclusions as to the age of the fish can be drawn 
from them. I am unable, therefore, to agree with Heincke, who states 
that the age of cod can be determined from the coracoid and scapula. 
I have found the bones of the operculum and skull equally unsuitable 
for the purpose here in view. In the vertebral column of a specimen of 
some size, parallel lines are distinctly visible in almost every part and on 
every process, including the walls of the anterior and posterior cavities, 
the neural spines, and the transverse processes, but I have found it 
impossible to use them as satisfactory indications of age. On the walls 
of the conical hollows of the centra numerous concentric lines appear, 
