STUDIES ON THE DIGENETIC TREMATODES., 403 
feature of difference between the dorsal and ventral papille 
is due to the fact that the dorsal wall of the sucker is not 
closely apposed to the dorsal body cuticle, but is separated 
from it by parenchymatous tissue. The dorsal papille in 
finding their way to the exterior have to pass through this 
layer, and thus around the base of each dorsal papilla a 
small swelling is formed by the parenchyma, and this 
swelling is absent in the case of the ventral papille, for at 
their origin the wall.of the sucker is contiguous with the 
cuticle and there is no intervening tissue. Still another 
point is to be remarked. ‘The ventral papille arise from the 
already noted anterior swelling of the sucker, but the dorsal 
papille arise from the main part of the sucker, immediately 
behind the swellings. This is indicated in fig. 2. This 
circumstance seems to necessitate a modification of the views 
of Braun and Looss on the origin of the papille. It can 
still be maintained that the anterior swelling, together with the 
papille, represent the almost undivided suctorial swelling in 
Rhytidodes gelatinosus (R.), but it is evident that in 
Stephanophiala laureata the process of transformation 
has gone much further than was supposed. Thus the division 
of the simple swelling has given rise, not only to distinct 
contractile papille, but four of these have been entirely 
separated from the original swelling and have been displaced 
backwards, 
The ventral sucker is situated near the junction of the 
anterior and middle thirds of the body. It is transversely 
oval and nearly twice as large as the oral sucker. Its trans- 
verse diameter is "50 mm. and the longitudinal diameter °43 
mmm., i.e. the diameter is about one seventh of the length of 
the body. Its depth is -16 mm. and occupies nearly the 
whole thickness of the body. ‘The wall has an average 
thickness of (057 mm. The histological structure is essenti- 
ally the same as that of the oral sucker, the muscle-fibres 
being, if anything, slightly stouter and the myoblasts pro- 
portionately less numerous. The sucker as a whole does not 
project much above the surface of the body. 
