Maddox, on Parasites of the Common Haddock. 89 
to be only 4 condensed textures of the infested being.’ ” Dr. 
Knox, 44 that it belongs especially to the parasite.” Mr. 
Goodsir’s brother, as regards the parasite in the liver of the 
sunfish, says, 44 May we not suppose them to be part of the 
original ovum, within which the animal was formed, and 
within which it passes its term of existence.” The special 
cyst of the Distoma in the nerves of the haddock, is described 
in the article from which the above remarks are quoted, as 
consisting of 44 three tunics : an external, which appears to be 
derived from the areolar texture of the infested animal, a 
middle and internal belonging to the parasite ;” 44 the second 
tunic is a fine transparent membrane which lines the first, 
and has in its turn its internal surface covered by an epi- 
thelial layer, which is the third tunic of the cyst. The 
epithelia are flat, irregular in shape, and somewhat opaque. 
The third or internal layer, formed by them, breaks up under 
the glass plates, so as to present rents or fissures passing in 
various directions over it.” 
I have not been able to satisfy myself of the correctness of 
these particulars, but rather regard the cysts as the results of 
a secretion from the surface of the parasite, in fact as Von 
Siebold describes for the Cercariae. 44 After a Cercaria has 
been for some time in the water, first creeping and then 
swimming about with manifest restlessness, it gathers itself 
up into a ball and emits from its whole surface a mucous 
secretion, which soon hardens, and since inside of this mucous 
mass the worm, coiled up into a little ball, turns round 
without stopping, invests it as it were in an eggshell.”* 
The secretion in the present case I believe to arise chiefly 
from the lower part of the body, for I have found in several 
specimens removed from the cysts a grumous granular matter 
exuded and adherent to this portion, and forming a layer at 
the surface of the body of some thickness ; also on wiping 
over the surface of the animal in water with a fine camel-hair 
pencil under the erecting microscope, a considerable amount 
of finely granular substance can sometimes be remarked. 
Moreover, I cannot detect any distinct tunics in the cyst, nor 
any epithelial structure as such, with nuclei coloured by 
carmine, or by maceration, liquor potassae, &c. &c. 
The outer portion seems to be of a condensed mucous or 
almost chitinous material, of a variable thickness and lined 
by a more or less transparent friable substance which, on the 
growth of the parasite in its expansion, splits up into 
irregular plates of some substance, having fissures that reach 
to the inner surface of the external or more condensed part. 
* Von Siebold on Worms, 1856-7. Pub. by The Sydenham Society, p. 20. 
