78 ILLINOIS BIOLOGICAL MONOGRAPHS [296 



The position of the genital pore as well as the organology depicts it as 

 distinct from Collyriclum. This study confirms the systematic position of 

 Brandesia given by Looss in that it is more closely related to the Pleu- 

 rogenetinae. Collyriclum is in some respects closely related to the Pleuro- 

 genetinae and in other respects to the Brachycoelinae. The diagnostic 

 characters of Collyriclum are so evenly distributed between these two sub- 

 families that it holds an intermediate place as shown in the table opposite. 



Whether the interpretation given above is the correct one remains 

 indeed a matter of conjecture and certainly lacks much of confirmation. 

 It is difficult to ascertain from an anatomical study of adult forms as 

 to whether acetabula are vestigial. The most immature Cyclocoelidae 

 studied by the writer show no trace of such organs. These forms belong 

 to Cyclocoelum obscurum. In more advanced stages of Cyclocoelum halli 

 the sucker is found practically as well developed as in the adult. Since 

 the material of the immature stage of Cyclocoelum obscurum was not well 

 preserved conclusions cannot be drawn from it. In the immature stages 

 of N otocotylus urbanensis studied by the writer the ventral glands were 

 found to develop after encystment of the cercariae and to show no rela- 

 tion in their development to an acetabulum. Much evidence on this 

 point can yet be obtained by the elucidation of this and other life histories. 



It is worthy of note, however, that in the Notocotylidae the oral 

 sucker is well developed in the cercariae as well as in the adult, but instead 

 of a single well developed acetabulum the condition is somewhat varied. 

 In Notocotylus quinqueserialis five rows of small sucking discs are pro- 

 vided. In N otocotylus attenuatum three rows of similar organs are present, 

 while in Nudocotyle and Paramonostomum no such sucking organs are 

 present. These species live in a similar habitat (intestine of the muskrat) 

 and under this condition have developed in the first instance different 

 numbers of these organs while in the latter case no- such structures have 

 been observed. Nudocotyle novicia, however, presents other striking differ- 

 ences which need not be considered here. In the cercariae of these forms 

 described notably by Cort (1914) and Faust (1918) no such organs are 

 found nor is there any indication of their early development, while in the 

 immature forms of Notocotylus urbanensis studied by the writer these glands 

 are found well along in development soon after being freed from the cyst. 

 The other organs of these cercariae correspond so well to the adult struc- 

 ture that there is little doubt as to the identity of the form. In this case 

 then the sucking discs are developed after the organism enters the defini- 

 tive host. A final decision of this question, however, must await further 

 evidence and experimental demonstration of the life history. 



The cases of reduction of sucking musculature cited by Cohn (1904) 

 and Odhner (1907, 1911) lead again to the question raised previously and 

 in the light of the theory of Cohn and Odhner it is difficult to determine 



