SEA-FISHERIES LABORATORY. 85 



more advanced is the tumour, the more deeply is it 

 charged with melanin. The latter may at first be 

 recognised as definite granules laid down within cells of 

 recognisable outline, but as the tumour grows the deposit 

 of melanin becomes denser, and finally the cells are no 

 longer apparent. The melanin formation is to be 

 connected, in some way, with the tendency for pigment 

 formation in the integuments of most fishes. If it is a 

 " metabolic habit " of this nature it may be more typical, 

 in man, of morbid growths in coloured races, or in 

 brunettes, than in white races, or in blondes. I do not 

 know whether or not this is the case. Melanism of 

 malignant growths has been observed in Skates, Rays, 

 Halibut and Cod, but it is more characteristic of the two 

 former species than of the two latter. 



Necrosis always occurs when the tumours attain some 

 size. Even in small growths, say in those of two or three 

 centimetres in diameter in Skates and Rays, there is 

 always very considerable softening and disintegration of 

 tissue. Melanin formation then attains a maximum, and 

 the tumour appears to be coal-black in section. When it 

 becomes much larger than this its central parts liquefy. 

 Usually there are no blood vessels in these malignant 

 tumours, and autolysis probably occurs. When the larger 

 tumours, say those of 5 to 10 cms. in diameter, are cut 

 open, the contents run out as an inky-black fluid with the 

 consistency of pus. A soft or liquid tumour of this stage 

 does not set hard when preserved in alcohol : its central 

 parts always remain soft and pasty. 



Distribution of the Tumours. 



Such are the general characters of malignant growths 

 in fishes. The specimen which I have now to describe 

 illustrates very well all these characters, and particularly 



