STUDIES ON. THE DIGENETIC TREMATODES. 421 
Bunodera is relegated to a separate sub-family, BuNoDERINE 
Pratt, including the rather anomalous genus Tergestia 
Stoss. 
In Crepidostomum the uterus appears to have under- 
gone a process of retrogression or degeneration, while 
Bunodera, and, to a less degree, Patagium display a con- 
dition altogether foreign to the ALLOCREADIIN», in which the 
uterus never extends beyond the anterior border of the first 
testis. In Crepidostomum and Acrodactyla the structure 
of the cirrus-pouch is not well known, but indications point 
to its being not unlike that of Stephanophiala. Buno- 
dera and Patagium again display a distinctly different 
type, with non-muscular wall and more or less highly- 
convoluted vesicula seminalis. The absence of muscle-fibres 
might be regarded as the result of a series of degenerative 
changes, but that is merely hypothetical. Further, in 
Bunodera the condition of the ova, in which a Mira- 
cidium larva is developed within the uterus, is very dis- 
similar from that of the ALLocrEapIINZ and Stephano- 
phiala. In Crepidostomum and Patagium the condition 
of the ova.is not known. 
The inclusion, therefore, of all these genera within the 
sub-family, BunopERIN®, as proposed by Looss and Heymann, 
is not without objection. They are possibly related, but how 
closely is not very apparent. Too great weight has hitherto 
been placed on their common possession of a circum-oral 
collar, and, as in the case of Rhytidodes, such a structure 
may .be present in a genus which cannot be included in the 
same sub-family. To consider the circum-oral collar as the 
diagnostic feature of the sub-family BunopERIN% would be 
a reversion to the now discarded system of classification by 
external characters. We must therefore look to the internal 
structure, mainly, for guidance. From this it is evident 
Crepidostomum Brn. and Helicometra Odhn., although he includes 
those genera in his sub-family. Pratt’s classification is obviously 
premature but it is of great help, and he is certainly correct in separa- 
ting Bunodera from the PsILosTtoMIN-». 
