NEW GROWTHS IN FISH. 283 



Microscopic sections presented very varying pictures according to the 

 particular part of the tumour from which they were taken. The central 

 part of the mass, after decalcification, could be recognised as consisting 

 of fibrous tissue in which a considerable deposition of lime salts had 

 taken place ; this mass surrounded and merged into the bony tissue of 

 the basi-hyal, and was penetrated in all directions by narrow blood 

 spaces. These spaces were filled with blood corpuscles and rounded 

 cells with large nuclei and distinct nuceoli ; the amount of surrounding 

 cytoplasm varied considerably in different cells, but was seldom great. 

 From the fact that these blood spaces were more plentiful in the outer 

 part of the central mass and did not penetrate to the centre, it would 

 seem probable that the hard fibrous tissue had first been formed and had 

 undergone partial calcification, and that then it had been invaded by 

 the formation of ingrowing capillary blood spaces. Other sections 

 from the softer parts of the tumour showed areas of loose and compact 

 fibrous tissue, and other areas undergoing myxomatous degeneration : 

 blood corpuscles and the rounded cells described above were present in 

 varying numbers in almost every part of the growth. The surface of 

 the marginal part of the tumour was irregularly covered with the 

 cutaneous epithelium which had a tendency to form ingrowths of com- 

 pact masses of epithelial cells, but did not show signs of becoming 

 epitheliomatous. The more highly cellular portions of the growth 

 presented the appearance shown in Fig. 6. Masses of rounded epithelioid 

 cells were present, and irregular channels containing blood corpuscles 

 could be distinguished between the cell masses. The boundaries of 

 these channels showed a more or less regular arrangement of the 

 epithelioid cells, which in places had a tendency to become elongated 

 in the direction of the long axis of the blood channel ; many of these 

 cells were also present among the corpuscles in the blood spaces. In 

 addition to these spaces with very ill-defined boundaries, other blood 

 channels with more definite walls, usually circular in section, and more 

 resembling capillaries, were present. These channels were bounded 

 by a very delicate sheath, but no endothelium within the sheath could 

 be distinguished. Comparatively few mitoses were observed in any of 

 the sections, so it is probable that the growth was not extending rapidly 

 at the time of examination. 



The tumour can obviously be diagnosed as an endothelioma, arising 

 from the endothelium of the blood vessels, and it appears identical in 

 structure, growth, and arrangement of the cells to similar endotheliomata 

 occurring in man. 



No metastases were present. 



