.80 THURLOW C. NELSON 



ried into the deep furrow and thence to the intestinal groove. 

 In this groove, or the intestine proper, the effective stroke of 

 the ciha is toward the posterior end of the body, and thus the 

 waste matter is carried to the outside. 



On the broad surfaces of the typhlosoles the effective stroke 

 of the ciha is inward toward the style sac, and somewhat in a 

 posterior direction as well. The cilia on the faces of the two 

 typhlosoles are not equally developed in all species. In Lamp- 

 silis I find that those on the major typhlosole are of about twice 

 the length of those on the minor. 



The regular transverse folds of the style sac, with their great 

 bristle-like cilia, have been described (p. 65). The effective 

 stroke of these is such as to put the style in rotation in a clock- 

 wise direction, and at the same time to push it anteriorly against 

 the gastric shield. 



Barrois ('89-'90, p. 356) believed that the style turned on its 

 long axis while being pushed forward into the stomach. List 

 ('02, p. 277), ignoring this statement of Barrois, expressed the 

 opinion that the function of the large cilia of the style sac was 

 to set the style in rotation, while pushing it forward into the 

 stomach. Hoffmann ('14, p. 533) states that the style of Tagelus 

 is rotated by the cilia of the style sac. In the text of none of 

 these authors is there any statement indicating that the rota- 

 tion of the style was actually observed. Their conclusions were 

 based merely on the presence of the co-axial layers of which the 

 style is built up. 



The secretion and formation of the crystalline style 



Regarding the point of origin of the crystalline style there is 

 the same lack of unanimity of opinion among the various inves- 

 tigators that characterizes their speculations regarding its func- 

 tion. In general, three structures have been considered as being 

 the seat of its origin: the stomach, the hepatopancreas, and the 

 epithelium of the style sac. 



The opinion of Huxley ('53) was mentioned in the historical 

 summary (p. 58). Milne-Edwards ('59, p. 362) argued from the 

 existence of the co-axial layers of the style that it must be the 



