Abbreviated data on morphology of monogenetic trematodes are 

 scattered in a considerable number of specialized works. The most im- 

 portant are the researches by Zeller (Zeller, 1872-1876), Cerfontaine 

 (Cerfontaine, 1814-1900), and Seitaro Goto (Goto, 1891 - 1917) who produced 

 a series of very substantial works which contain a significant amount of 

 morphological material along with their systematic material. 



Recently, Brinkmann (Brinkmann, 1940-1954) published a 

 series of works which have significance for Monogenoidea and which are 

 based, not only on external characteristics, but also on detailed mor- 

 phological analyses of interior structures. 



12 



Literature data and especially the results of personal research 

 were utilized for the present essay. 



Sizes. In the majority of cases the sizes of the monogenetic 

 trematodes usually vary between the lengths of 0. 03 to 20 mm, and only 

 in rare cases do they reach a larger size. Thus Capsala martinieri Bosc 

 (Fig. 1) reaches 30 mm in length and 25 mm in width, Squalonchocotyle 

 sonnniosi (Causey) has a length of about 25 mm and probably Sq. borealis 

 (Beneden) (Fig. 2) reaches up to 30 nam, etc. One can consider it a general 



Fig. 1, Capsala martineri Bosc, adult worm. 

 (According to Price, 1939). 



rule that marine forms are larger than fresh-water forms. It is necessary, 

 however, to note that the naeasurement of size is hampered by the fact that 

 the body of monogenetic trematodes is capable of contracting and stretching 

 excessively. Most of the species can stretch almost tvice, and contract as 

 much in relation to the normal condition of their bodies. Thus, Dactylogyrus 

 auriculatus (Nordmann) (Fig. 3) which is about 0. 5 mm in the normal state 

 can stretch to 1 . 2 mm and contract to 0. 3 mm. 



