38 ILLINOIS BIOLOGICAL MONOGRAPHS [142 



small degree of movement. Internally the capsule is lined by a delicate 

 membrane through which the teeth project from the capsule wall while 

 externally there is a covering of granular material and the cuticula. When 

 variations of this capsular structure arise, it is mainly in the change of 

 form among the teeth and cutting plates. The papillae are six, arranged 

 bilaterally near the edge of the capsule with three on each side {Ancylostoma 

 caninum Ercolani Fig. 40). 



The head of the larva of the above form is radially symmetrical regard- 

 ing the triquetrous mouth opening and the papillary arrangement, two to 

 each sector, however the presence of two mid-lateral ridges alters the 

 symmetry to the same as exists in the adult. Indeed, none other than 

 bilaterality could exist in such a structure as the adult capsule. The 

 question of the origin of the capsule can be only partly answered from the 

 larval forms. In the young free-living larva the pharynx is a rather long 

 unarmed tube entered apparently by the triquetrous opening between the 

 three fused lips. If this interpretation is correct, then the buccal capsule 

 arises from a fusion of lips in connection with a large pharynx, as is the 

 case with some of the free-living forms (Figs. 18, 19, 23). 



In contrast to the hookworm capsule is the type found among the 

 Sclerostomes which have the mouth opening anteriorly terminal. The 

 general anatomy of the cephalic region is the following: the cuticula or 

 skin is considerably thickened around the edge of the mouth and con- 

 stricted by a groove which produces a fold of cuticula, the mouth collar. 

 The anterior edge of this structure becomes split up into a very character- 

 istic and delicate fringe which Looss calls the "external leaf crown" the base 

 of which rests on the edge of the buccal capsule. There are six cephalic 

 papillae disposed radially and equally distant from each other. They do, 

 however, shift at times and assume a bilateral arrangement. The medial 

 lateral ones are slightly different from the other four rather submedial 

 papillae which possess cuticular points. The capsule is formed of a homo- 

 geneous substance lined by a delicate granular membrane and along the 

 mid-dorsal wall runs the gutter or duct of the dorsal esophageal gland, while 

 at the base on either side there may be two rounded inward pointing 

 plates opposed by two similar ones on the ventral side {Scleroslomum 

 equinum Miiller) (Fig. 39). These both, however, may be absent or in other 

 genera replaced by three three-flanged teeth arising symmetrically from 

 the floor of the capsule (Triodontopliorus minor Looss) (Figs. 26 and 38). 



The symmetry of the former specimen could not be other than bilateral 

 but of the latter, were it not for the dorsal gutter and a few minor external 

 details, the symmetry would superficially pass as radial. As in previous 

 forms, the striking specific differences arise from modifications of the 

 "leaf-collar," of the general outline of the capsule, and of the armatures 

 arising from the floor and walls of the buccal cavity, but at no time is the 

 symmetry radial in the sense of including other than the most superficial 

 details. 



