Anatomical structure of Aspidogaster conchicola. 495 



not present in Aspidogaster. It is true that the anterior end may 

 function as a sucker as when the animal cleaves to a glass slide by 

 flattening out its trumpet- shaped mouth against the glass. That it 

 is so used in its natural habitat I can not affirm. Young animals 

 seem to use the mouth funnel for this purpose much more frequently 

 than adults. In the embryo the mouth sucker is apparently as distinct 

 a structure as the posterior sucker, and in fact Vogt mistook the 

 posterior sucker for the head end (anterior end) of the embryo. This 

 sharply contoured appearance of the anterior sucker is not simply 

 external, for in longitudinal sections of the embryos the nuclei of the 

 cells bounding the posterior limit of the head sucker are in a definite 

 semicircular form; but there is never a limiting-membrane. The 

 embryo moves with a looping motion and often clings to the surface 

 of older Aspidogasters by its mouth. 



Supported by these considerations as well as by some facts of 

 its structure it cannot be taken far amiss if we call the anterior end 

 a mouth sucker although we must consider it as a much less specialized 

 organ than the mouth sucker of nearly all Trematodes. It is likely 

 that its form in the adult has more relation to the habits of nourish- 

 ment than to those of locomotion. By closing in the outer rim of 

 the sucker a considerable quantity of fluid can be enclosed within the 

 animal and then by a swallowing motion in the pharynx accompanied 

 by a contraction of the mouth sucker this fluid can be forced into 

 the intestine. Also, not seldom, the anterior end of the foot comes 

 to take part in the procuring of nourishing material in that it makes 

 a motion towards and across or into its mouth as if pushing something 

 into and then closing up the mouth, somewhat as a child would hold 

 in a big mouth-full with its hand. It is also probable that it can 

 procure more epithelium or blood cells or even by a sucking motion 

 rub away and collect more by such a structure than it could other- 

 wise do. Keber wrote in 1851 that Aspidogaster by sucking tears 

 off epidermis cells. 



The walls of the mouth sucker are round the margin thin, but 

 increase in thickness as they are continued backwards until the inner 

 surfaces meet anterior to the pharynx. Looking into the mouth 

 opening, as the sucker is attached to a cover glass loosely suspended 

 on wax feet, one sees how the cuticle is thrown into folds curving 

 inwards from the rim to the narrow opening leading to the pharynx. 

 When the animal expands the mouth cavity to its full extent of course 

 these ridges disappear. The outer shape of the sucker (Fig. 1, 3) 



