l8 OSBORN. [Vol. XVIII. 



beyond. These parts are not the same in the family at large. In 

 Macraspis there is a short unpaired bladder (as in trematodes 

 generally) ; in Aspidogaster the collecting vessels are slightly 

 swollen near the tips, and after meeting diverge and open by two 

 separate and distinct pores; in Cotylogaster occidentalis there are 

 two separate very thin-walled bladders with a single median pore, 

 which opens at the base of the dorsal cone (Xickerson '99) ; in 

 Stichocotyle the function of a bladder is assumed by the very 

 large collecting vessels, which communicate with the exterior by 

 means of two very narrow tubes which join and form a single 

 short and very slender one. In all these cases the excretory 

 opening is located posteriorly and dorsally. To return to Coty- 

 laspis, the excretory pore is an indentation of the cuticle (Fig. 19) 

 which leads by a short passage into the bladders. Their .walls are 

 lined in the parts nearest the exterior with a layer indistinguishable 

 from the cuticle of the body in general, but in the deeper parts the 

 lining is a true nucleated epithelium, which is directly continuous 

 with that of the collecting vessel. Fig. 20, which passes through 

 the junction of the collecting vessel and the bladder, leaves no 

 room for doubt on this point. It is an important further fact 

 that in the wall of the bladder, between the epithelium and the 

 cuticle, we find cells (Fig. 21) in which the cytoplasm is still 

 recognizable, but the nucleus shows signs of degeneration, and in 

 place of a distinct nuclear membrane, nucleolus and scattered 

 chromatine grains, we find a formless mass deeply staining and 

 having the size and position of a nucleus. If we accept these as 

 indication of cell-degeneracy, then in this place at least the cuticle 

 seems to be a modified epithelium, a fact in harmon}- with the indi- 

 cations of its origin given by that of the cesophagus. 



In addition to this lining the bladders possess muscular fibers, a 

 distinct sphincter muscle can be seen (Figs. 18, 19), and in the 

 wall are scattered longitudinal fibers continuous with those of the 

 collecting vessel. The parenchyma condenses around the bladders, 

 where we find a denser aggregation of fibers and nuclei. 



In life the bladders simultaneously pulsate somewhat rhythmic- 

 ally. Pulsations were noticed in Aspidogaster by Huxley '78, 

 who states that the entire collecting vessel pulsates, which is not 

 the case in Cotylaspis. At the moment of contraction the pore 



