258 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



exigencies of their position, confined as they are by the papillae, so 

 that they lie frequently transversely with their narrow ends extend- 

 ing downwards. (Fig. 2.) 



The ventral surface is characterized by the total absence of pig- 

 ment, which is true of the corium as well as of the epithelium. 



ABNORMAL CONDITION OF THE SKIN. 



In two successive Springs I have observed certain tumours of the 

 skin of a somewhat spongy appearance which do not appear to be 

 confined to any particular region of the body but are commonest on 

 the head and in its neighbourhood. I have, however, observed them 

 on various parts of the trunk. It is possible that these are to be seen 

 also at other times of the year, but, as they have only attracted my 

 attention in Spring, I supposed at first that they might be somewhat 

 similar to the ' Perlbildungen ' described by Leydig, or comparable 

 to the more extensive epidermal changes which take place at the 

 breeding time in many Cypxinoids. That they are not frequent is 

 sufficient indication that they are not normally recurring structures ; 

 and Prof. Leydig informs me that the histological change is not of 

 the same nature as that which characterizes the ' Perlbildung.' 

 Their appearance and the condition of their occurrence appear to me 

 to exclude their being merely a reparative proliferation after a wound, 

 and I have arrived at the opinion that we have in these tumours 

 something similar to Epitheliomata. 



If a portion of such a tumour be placed in Midler's fluid over night 

 and the epidermis pencilled away, the slender papillae stand up from 

 the corium so as to form a sort of pile on its surface. The dissocia- 

 tion of the epidermis takes place much more readily than in normal 

 skin, partly owing to the fact that the superficial layers, especially 

 that bearing the cuticular border, have disappeared, partly owing to 

 infiltration into the interepithelial spaces. The altered papillae 

 instead of being short, simple and cylindrical, may attain a length of 

 over 1 mm., be much branched, and sometimes flattened and palm- 

 ately branched. For the nourishment of the increased epidermal 

 surface, the vascular networks of the papillae are much richer, and an 

 increased number of pigment cells are observable. Although the 

 papillary layer of the corium is thus increased in thickness, the 

 fibrous layer is much thinner than in the neighbouring unaffected 

 parts of the skin. The nature of the cells, which fill up the inter- 



