86 THURLOW C. NELSON 



In those lamellibranchs where the style lies in a separate 

 caecum, distiiict from the intestine, there are marked differences 

 from the type we have been considering. Since there is no con- 

 nection between the style caecum and intestine, there is no means 

 by which food particles could be incorporatisd into the structure 

 of the style. Investigators who have examined the styles from 

 this type of mollusc state that food particles are universally 

 absent from them. In Pholas, for instance, following Barrois 

 ('89), the style has a central core of bubbly mucous, entirely 

 free from foreign particles. I find the same is true of JVIartesia. 



Mitra ('01) noted the inner core of food matter in the style of 

 Anodonta, but thought that it was due to some imperfection in 

 the method of storing the ferment in the style sac. The absence 

 of such an inner core in the styles of Pholas was held to be the 

 result of a superior, more differentiated mechanism for storing 

 the ferment and for passing the food material through the ali- 

 mentary canal. 



A further difference in this species lies in the fact that the 

 style is comparatively short and thick and that the smaller and 

 not the larger end projects into the stomach. I have found 

 this condition in Martesia, where the style is of relatively enor- 

 mous proportions, comprising as it does a large part of the vis- 

 ceral mass (fig. 8). In both of these forms the style resembles 

 roughly a policeman's club in shape. 



The relatively large style in Teredo and other boring molluscs 

 was noted by Deshaj^es (48) and Quatrefages ('49). 



I have been unable to find anj^ reference in the literature as 

 to the exact location of the secretory activity in forms possessing 

 a separate style caecum. We have seen that Mitra's suppo- 

 sition that the hepatopancreas is the source of this secretion is 

 entirely opposed to the facts as determined for the species thus 

 far considered. That this supposition is equally invalid in the 

 type under consideration must be evident from the anatomical 

 relations of the hepatopancreas to the style caecum, as found in 

 Martesia (fig. 8). To my knowledge no channel exists through 

 which a secretion from the hepatopancreas could be applied to the 

 surface of the style, even if the effective stroke of the cilia of this 



