BvLh. U. vS. B. v., 1919-20. 



Plate XVI. 



Fig. I. — Filaments of gill of fresh-water drum with hea\'^' natural infection of 

 Plagiola donaciformis. Estimated total number of glochidia carried by fish 

 4,Soo. 



'M 



Fig. 2.— Glochidia of washboard mussel. Quadrula hcros. on FiG. j.— Section through vacated cysts on gill filaments; 



fin of fresh- water drum. Cyst very much enlarged. ' Quadrula ebcnus on river herring. 



