EOBSON : STYLE-SAC AND INTESTINE IN MOLLUSCA. 43 



presence of a style or sac in the Rhachiglossa or Toxoglossa. From 

 the figures of Nassa, Buccinum, and Murex, given by Simroth/^ 

 there woald appear to be no sac large enough to lodge a style, 

 though the slight hollowing out between cardiac and pyloric orifices 

 in Murex is referred to by him as a coecum. Collier's statement that 

 a style occurs in Murex vertagus may be regarded in the same light 

 as his statement regarding Trochus turritus, though we have more 

 positive evidence in this case, as vertagus is a well-known specific 

 name of the Vertagus subgenus of Cerithium and at least one early 

 author (c/. Tryon ^°) has referred a Cerithium to Murex ! We have 

 seen above that a style is very largely restricted to the Tsenioglossa, 

 to which group Cerithium is referred. 



We have now to discuss shortly a few ambiguous cases before 

 proceeding to our general considerations. As a preliminary to this 

 a certain amount of definition is necessary. We have considered 

 so far cases where we find either a definite style or a sac lying 

 alongside the pylorus, and sometimes communicating with the latter, 

 which, for various obvious reasons, may be considered as the sac 

 in which the style is formed. This definition is necessary because the 

 style is a transitory structure, disappears under certain physiological 

 conditions, and is rapidly dissolved by fixation reagents. In its 

 absence we may argue from the presence of the characteristic sac. 

 But on this point due discrimination should be exercised 

 before all pyloric cceca are accepted as style sacs. For 

 that reason T have qualified the case of Ampullaria. 

 A similar caution has to be exercised with regard to the so-called 

 fleche tricusjnde. Moore " (1898) pointed out the error of identifying 

 this structure with the crystalline style, though he fell into the error 

 of assuming that the fleche of older authors really meant the whole 

 cuticular lining of the stomach, which had becomj.e detached from 

 the stomach wall. It would seem, however, that the fleche is the 

 strongly marked cuticular ridge often found in the wall of the stomach 

 of many Prosobranchs. 



We have described several obviously doubtful cases above, such 

 as Lithoglgphus, in which, although we know a style occurs, the 

 precise position of the latter is doubtful. There are, in addition, 

 certain cases in which we should suspend judgment as to whether 

 a style occurs at all. In Conchole2')as Haller^ (1888, pp. 110, 111), 

 apparently considers there is a style owing to the similarity between 

 the area assumed to secrete the style in that genus and in Fissurella. 

 He found no style, however, and there is apparently no coecum. 



There is, finally, a third category of doubtful cases. Collier states 

 that there is a style in Stromhus, and Haller ^ (1893) refers to a 

 coecal outgrowth in that genus and in Rostellaria ; though he does 

 not refer to any style. Woodward (1893, p. 147) says that this coecum 

 is obviously the homologue of the crystalline style-sac oi Pterocera. 

 I do not consider that this is so obvious as Woodward thought. 



