84 THURLOW C. NELSON 



ing abundant food material will ordinarily show a style of very 

 dark color, due to the large central core of food material. On 

 account of the irregularity in the arrival of this escaped food 

 matter at the end of the caecum, this inner core may vary con- 

 siderably in thickness throughout its extent (fig. 14). On the 

 other hand, when an animal has had abundant food for a long 

 period and has not been actively feeding just prior to examina- 

 tion, the style may be practically free from all food material 

 and may possess a very thin core of whitish mucus. 



Considerable variation in the length of the secretory portion 

 of the typhlosoles occurs in different species. In some this 

 region, instead of occupying most of the extent of the typhlosole, 

 is quite restricted. As a result, the superficial layers of the style 

 are applied much as a thick tape might be wound around a stick. 

 Such a condition may occur in Mactra where, according to Kel- 

 logg ('92, p. 402), the outer lamellae of the style may actually 

 be unwound from the core. 



I have found a somewhat similar mode of accretion when 

 feeding Modiolus a fine suspension of carmine grains. The coarse 

 grains of color passed down the intestine to the diverticulum 

 where they were built into the central core of the style. The 

 finer grains, however, were carried across the faces of the typh- 

 losoles at one point and applied to the surface of the style. 

 As a result, this organ when removed much resembled a barber's 

 pole, with the spiral band of bright red carmine grains wound 

 around it. 



One interesting anomaly may be described here as shedding 

 some light on the manner in which the superficial layers of the 

 style are laid down. A style of Lampsilis anodontoides was 

 found to which an air bubble had become attached at some dis- 

 tance from the end of the sac. As the style was rolled round and 

 round this bubble was flattened, and over it was deposited a thin 

 layer of clear secretion cementing the bubble securely in place 



(fig. 17). 



The description of the formation of the style as given above 

 applies to all forms in which the style sac is incompletely sepa- 

 rated from the intestine by the typhlosoles. In the more primi- 



