the entire excretory apparatus acquires a netlike character where a large 

 part of the small as well as the large canals are equipped with a powerfully 

 developed ciliated cover. Among a majority of forms the excretory system 

 is colorless but among representatives of the genus Calceostoma the walls 

 of the vessels and their liquid contents are often darkly tinted. 



0.1mm 



Fig. 69. Polystoma integerrimum 

 Froelich, sagittal section through 

 the intestinal branch. The remnants 

 of the frog's red blood corpuscles in 

 the process of being digested appear 

 in black in the cells of the intestinal 

 epithelium. 



Fig. 70. Diplectanum aculeatum 

 Parona and Perugia, excretory 

 system of the anterior end of the 

 body of an adult worm from the gills 

 of Corvina nigra Cuv. and Val. 

 from the region Karadaga (Black Sea). 

 (Semi -diag rammatically ) . 



The terminal parts of the excretory system are located at the 

 level of the pharynx or somewhat lower. They consist, on each side of 

 the body, of a single canal which often forms, at some place along its 

 length, a more or less well-developed contractile bladder--excretory 

 bladder equipped with special musculature. The excretory vesicles or 

 bladders open to the outside by independent apertures which are located 

 either laterally or more often dorsolaterally. The snnall duct which is 

 usually present between the excretory aperture and the bladder is equipped 

 with a powerful muscular sphincter. Excretory vesicles are well-developed 

 among many monogenetic trematodes but weakly noticeable among Mazo- 

 craeidae, Microcotylidae, and families related to them. 



45 



