288 GILBERT C. BOURNE. 



tissues in contact with these structures than has Mitra.^ He 

 describes the "fleche tricuspide " of Don ax as forming a 

 complete lining of the cavity of the stomach, and as being 

 more or less adherent to the anterior end of the crystalline 

 style. He does not recognise any gland cells in the epithe- 

 lium of the stomach, but suggests that the " fleche tricuspide" 

 is foi'med from a granular mass detached from the ends of the 

 epithelial cells, and gives some not very satisfactory figures 

 in support of his statement. He further suggests that the 

 function of the " fleche tricuspide " is to protect the walls of 

 the stomach from injury. In his description of the ca3cum of 

 the crystalline style of Donax, Barrois calls attention (and 

 as far as I can determine he is the only author who has done 

 so) to the existence of a groove lined by a modified epithe- 

 lium, running the whole length of the right side of the csecuni 

 of the crystalline style, from its origin from the stomach to 

 its extremity. There is a similar groove along the right side 

 of the caecum of Enigma, showing the same histological 

 characters as those described and figured by Barrois in 

 Donax. I have given a careful drawing of this groove and 

 the adjacent parts of the wall of the caecum in fig. 22. As 

 regards the characters of the epithelial cells, it corresponds 

 so exactly with Barrois' description that I need give no 

 further account of it, except to call attention to the extremely 

 long cilia borne by the short cells lining the bottom of the 

 groove, and the short and fine cilia borne by the tract of 

 modified columnar cells on the upper side of the groove. 

 These are not described by Barrois, who says on the contrarj'-, 

 '' toute la surface epitheliale est tapissee de cette epaisse et 

 forte couche de cils vibratiles d'ont j'ai parle a maintes re- 



* Mitra appears to have been very imperfectly acquainted wiih tiie researches 

 of his predecessors on this subject, and his quotations of literature are mostly 

 derived from text-books. Had lie read Barrois' memoir, he would have found 

 that as early as 168G v. Ileide suggested that the crystalline style was sub- 

 servient to digestion: "aliquendo cogitavi hunc stylum suppeditari alimini 

 fermentum." Barrois gives a very interesting account of the various views 

 that have been held on the origin and function of the crystalliue style. 



