118 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
directions, so that the cells themselves are sometimes cut 
in transverse section; but among them there are other 
smaller spindle cells lying with their long axes in the 
plane of the section. When the larger spindle cells are 
cut transversely they often appear to be surrounded by 
annular spaces. Small spherical cells are also present, 
but these are relatively few in number in the fully 
developed tissue. 
The Growing Edge of the Tumour. 
Obviously it is only by examination of the growing 
edge that we can be certain whether or not the tumour 
is malignant in nature. I think there is no doubt that 
this is the case with the growth in question—it is a truly 
malignant sarcoma. Fig. 1, Pl. IV, represents a 
vertical section of the skin of the Ray at a distance of 
about two inches away from the tumour: the region of 
the skin from which the section was made can be seen in 
the photograph (Pl. III) and also the region of the edge 
of the tumour itself which was examined. The structure 
of the skin of an Elasmobranch fish is well known, but I 
reproduce an original drawing for the purpose of com- 
parison with the affected area. The epidermis is rather 
thick, and consists of cells roughly columnar in shape at 
the base of the layer, but polyhedral in shape nearer to 
ce 
the surface. The cells are “‘ prickle-cells,”’ that is, they 
are joined together by delicate protoplasmic filaments. 
Sometimes the cells are very closely apposed, but the 
filaments can nearly always be seen. ‘The epidermis rests 
on a thin layer of areolar connective tissue, and just 
underneath the bases of the cells forming the lower 
boundary of the epidermis there is an interrupted layer 
of black pigment cells. These occur everywhere in the 
skin of the fish, and in the black spots on the anterior 
