this, the middle hooks of the disc remain on its posterior end ( Heteraxine) . 

 The second type of asynnmetry results in more or less equal nunnbers of 

 valves on both sides of the middle hooks in such a way that the right side 

 of the disc with its attaching clamps performs, so to speak, a movement 

 or motion with the middle hook as a pivot point, thus establishing a single 



line of clamps with the left half. 

 The final result is a straight line 

 of clamps with the middle hooks 

 located in the middle and at a 

 sharp angle to the longitudinal 

 axis of the body of the animal 

 (Axine, Fig. 9). The question 

 relative to the formation of asym- 

 metrical discs is studied in de- 

 tail, although very briefly , in 

 the work of U. A. Strelkow 

 (1953). The number of clamps 

 usually varies from eight to 

 several hundred. The sizes in 

 one individual are more or less 

 the same, although there are 



species in which some of the 

 clamps are much larger than j 



the others (e.g. Pseudoanthocotyle, 

 A nthocotyle , Figs, 41, 42). 



The correlation between 

 different types of attaching for- 

 mations in the various groups of 

 moncgenetic trematodes is not the 

 same. 



34 



Fig. 40. Heteraxine heterocera (Goto) 

 adult worm 



The size of the little line 

 indicates the natural size of the worm. 

 (According to Goto 1894). 



Gyrodactylidae, Protogyro- 

 dactylidae , Dactylogy ridae , Amphib - 

 dellatidae and Tetraonchidae have 

 only chitinous attaching apparatuses. 

 The disc of these forms is more or 

 less strongly delineated from the 

 body and it is flat or concave; but not suction type. Lateral and middle hooks 

 are located on the disc. In some instances, middle hooks are absent (in 

 the genera Isancistrum, Fig. 43; Acolpenteron , Fig. 44; Anonchohaptor , 

 Fig. 45). Wherever they exist, chitinous joining apparatuses are also 

 usually evident with the hooks, nevertheless, there are forms with middle 

 hooks but without joining plates (for instance, Protancy rocephalus , Fig. 46). 



27 



