Excretory System . The excretory system has been studied 

 comparatively poorly. As opposed to the system of digenetic trerratodes, 

 among Monogenoidea it apparently does not have systematic significance. 

 In essence, the excretory system is composed of three parts: Protonephridia 

 and their capillaries and system of ducts including basic trunks and end 

 parts, which connect the excretory system with the outside. The proto- 

 nephridia of monogenetic trematodes are in the shape of the usual end cells 

 with ciliary flame. The capillaries leading from them resemble thin-walled 

 pipes, often bearing on their walls ciliated epithelium as among the 

 Turbellaria. Apparently these capillaries are intracellular formations. 

 The number and disposition of these flame cells have been studied very in- 

 sufficiently. The number of terminal protonephridial cells varies among 



O.Ihm 



Fig. 67. Squalonchocotyle spinacis 

 (Goto), cross section through the 

 intestinal branch. Enlarged 204 

 tinnes. (According to Goto, 1894). 



Fig. 68. Nitzschia sturionis (Abild- 

 gaard), cross section through the 

 intestinal branch. Worm from the 

 gills of Huso huso (L. ). 



the adult forms (among the young ones see chapter on embryology). Thus 

 in the anterior end of Diplectanum the number of flame cells, according to 

 our observations, is not less than six on each side (Fig. 70). The capil- 

 laries of protonephridia empty into canals which successively increase in 

 size and merge together to form two main ones which are loacted along the 

 sides of the body. The main canals stretch from the anterior end to the 

 posterior end and sometimes reach into the attaching disc and return to 

 the anterior end, often intertwining with its first half. The relationships 

 between both halves can be very complex. Among the nnajority of Dactylo- 

 gyridae, Monocotylidae, Capsalidae, and Polystomatidae and basal trunks 

 in the anterior part of the body at the level of and somewhat higher than the 

 pharynx form a rather complicated wavy part and join by cross commissures 

 so that its excretory system is no longer separated into right and left inde- 

 pendent parts but becomes unified (Fig. 71). Apparently among a number 

 of forms there are similar connections also at the posterior end of the body, 

 as for instance in Monocotyle ijimae Goto (Fig. 72). Among Calceostomella 

 inermis, Parona and Perugia, basic ducts are faintly noticeable because 



p. 50 



44 



