32 MONOGRAPH OF THE FRESH WATER IH. 



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. Respiratory 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. 



