300 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



and portions of muscle tissue were examined, but no 

 trace of myxosporidia could be detected. The gills, too, 

 were quite normal. The skin growth was examined 

 further for the presence of Infusoria, such as Costia. 

 Costia necatrix produces appearances on the skin of 

 various fishes not unlike that observed in this case. In 

 fact, it was possible to eliminate the possibility that 

 sporozoan or infusorian parasites were responsible for the 

 condition. The possibility that bacteria were concerned 

 was also considered, but a search for these was unsuc- 

 cessful, and I had no opportunity of examining fresh 

 material. 



Sections of the skin, including portions of the growth 

 were then made and stained with methyl-blue-eosin, and 

 Heidenhain's iron haematoxylin. 



Part of such a section is represented in fig. 1, pi. VIII. 

 It will be seen that the skin is very much altered. The 

 scales are in some cases quite displaced, and may even be 

 seen buried up in the tissue of the tumour. The dermis 

 is always quite unaffected ; whatever the disease is it 

 affects only the epidermis. This latter layer is quite 

 changed. In a normal fish it consists of roughly poly- 

 hedral cells lying close together, and contains large 

 mucus cells included among the others. At the base is 

 a very regular layer of cubical cells, and at the free 

 surface of the skin the epidermal cells become flat and 

 horny. The tissue of the tumour replaces the epidermis, 

 which, as a normal structure, has entirely disappeared. 

 Instead of it we see a densely compacted mass of smaller 

 cells. These are arranged in aggregates somewhat 

 resembling tubercles. In the axis of each tubercle is a 

 core of fibrous tissue, with a structure very difficult to 

 determine ; and here and there cavities containing groups 

 of small bodies, not unlike, in size and shape, masses of 



