16 ILLINOIS BIOLOGICAL MONOGRAPHS [296 



is undoubtedly a feature of distinct taxonomic importance, and the work 

 of Odhner is an advance step in the formation of a natural system and 

 the final classification of the monogenetie forms. Since the arrangement 

 of Monticelli, based on the character of the adhesive apparatus, so nearly 

 agrees with that of Odhner which in reality is based on the presence or 

 absence of a genito-intestinal canal, it appears that both these features 

 are of large importance in the taxonomy of the group. Present evidence 

 is insufiBcient to decide which is of greater significance. Further study 

 may show that there is complete agreement in classifications based on 

 both features. 



Odhner (1912) argued that the removal by Monticelli of Sphyranura 

 from the family Polystomidae on the basis of the difference in number 

 of suckers was not justified. As previously stated, the writer agrees with 

 Odhner that the seminal receptacles of Sphyranura are homologous with 

 the vaginae of Polystoma, and the agreement in type of genital ducts in- 

 dicates a closer relationship between these genera than is assigned in the 

 system of Monticelli. Sphyranura undoubtedly should be placed with the 

 Polyopisthocotylea. There are, however, wide and fundamental differ- 

 ences between it and the genus Polystoma, and while future researches 

 may discover intermediate forms which will make it possible to include 

 them with certainty in a single family, for the present such a grouping is 

 hardly justified and the two families should be retained, altho the name 

 Dicotylidae of Monticelli does not conform to the rules of zoological 

 nomenclature. 



THE GENUS POLYSTOMA 



The family Polystomidae as considered in this paper contains only 

 the genus Polystoma. The members of this genus are widely distributed, 

 species having been described from aU the continents except South 

 America. The species are not only widely distributed geographically, 

 but also vary widely in type of host and in locatisn within the host. 

 They are parasitic in the urinary bladder of frogs and toads and on the 

 gills of frog larvae, and also infest the urinary bladder and pharyngeal 

 cavity of many species of turtles. 



The structure and development of Polystoma integerrimum has been 

 investigated by Stieda (1870), ZeUer (1872 and 1876), WiUemoes-Suhm 

 (1872), Halkin (1902), Goldschmidt (1902), and Andre (1910). Zeller 

 (1876) described two forms of P. integerrimum, one which became ma- 

 ture in the urinary bladder of the frog, and the other which became, ma- 

 ture on the gills of the frog tadpole. These two forms of the parasite 

 show wide differences in size and internal structure. The form which 

 becomes mature in the urinary bladder is much larger, has a lobed 

 testis, external vaginae, and a long coiled uterus which contains many 



