812 
PROCEEDINGS OF THE SOCIETY. 
occur mostly on the blind side, especially in the axil of the pectoral 
fin, on the side of the head, and even sometimes within the mouth, 
reaching a size of over 1 in. in length and 1/2 in. in diameter. The 
lower operculum is also a common site for these tumours, which some- 
times extend within it and prevent its closing. If the skin is stripped 
from the body the eggs are found closely adherent to it and imbedded in 
it, while if only a few are present they are quite free from the subcu- 
taneous connective tissue. But in the case of the larger “ tumours,” 
there is a very close connection both with the skin and with the connec- 
tive tissue ; and if the mass is cut across it bleeds freely from various 
points, showing that there is a considerable vascular supply to a tissue 
which is distributed between the eggs. On a few fish affected, as well 
as on one without any of the eggs under its skin, I have found small 
depressions, opening outwards, with rough edges, and in course of 
healing, whence probably such bodies have escaped. But this is 
evidently a rare occurrence, as a flounder with many of these bodies on 
it was kept alive for four weeks, and none of them were set free. 
On microscopic examination the bodies present all the characteristics 
of eggs. A perfectly smooth pearly white membrane, with a radial 
striation in its inner layer, or zona radiata, encloses a granular material 
which gives all the staining reactions of yolk. There are usually fine 
fibrillas plainly visible, due to the coagulation of the substance, which 
when pressed from a fresh specimen, is fluid and milky in appearance. 
In two cases only have I found any development of these eggs, and in 
each of these the blastoderm had nearly completed the investment of the 
yolk ; each of these eggs was lying singly in the skin, the pigment layer 
being as usual over them, and reflected so as nearly to meet beneath 
them. In one case there were spaces in the skin around the developing 
egg, whence others had escaped, leaving portions of the egg-membrane 
clearly recognizable in section. In the large masses there are found, 
besides the eggs, whose mutual pressure gives them a polygonal appear- 
ance in section, though in other respects they wholly resemble those 
which occur singly, a connective tissue of various kinds ; and in most 
cases, always when the tumour is large, a plentiful vascular supply. 
This connective tissue is especially abundant near the base of the 
tumour, where the eggs seem to be not so closely packed. It consists of 
numerous small round nucleated cells, which are usually present in 
great numbers, and besides these there is frequently a more advanced 
tissue, spindle-shaped and stellate cells, and sometimes mucoid tissue. 
Thin-walled vessels pass between the eggs, and frequent haemorrhages 
from them leave either masses of red nucleated blood-corpuscles, or 
pigment. These haemorrhages are probably due to mechanical irritation 
of these tumours, which are very much exposed to violence, especially 
when on the under side of the fish. In the large tumours the elements 
are of a fairly constant size. They appear healthy and never appear to 
be breaking down or undergoing disorganization. But in no case has an 
egg in process of development been found in such a mass, nor does the 
covering skin show marks of eggs having been set free from it. 
In one case Prof. MTntosh found an adult specimen of Diplozoon 
paradoxicum in one of these tumours, but neither this nor any other 
parasite is commonly present. 
