32 MONOGRAPH OF THE FRESH WATER nT 
to the posterior part of the abdominal cavity. They not only differ from ovaries 
by their shape, but also by their color, which is generally deep brown, contrasting 
with the yellowish appearance of the ovaries. 
§ 11. Resprratory APPARATUS. 
This apparatus is composed of four branchial bony arches provided upon their 
convexity, with respiratory fringes in full activity. A fifth rudimentary row of 
fringes may be seen within the thickness of the membrane lining the inner wall of 
the opercular; but these fringes are not free and take no part in the aerification of 
the nutrient fluid. On each side, and internal to the fringes, there is along the 
concavity of the arches, a row of tubercles covered with minute card-like teeth, 
perhaps only needle-like asperities, for they are not inserted. on the tuberculous 
bone, but belong to the overlying membrane, to which they adhere when the latter 
is removed. ‘The inner arch possesses only one row of these tubercles, being 
united to the hyoidean apparatus by a membrane which leaves to the arch but 
little motion. 
