lfl24 J Lazier: Morphology of Digestive Tract of Teredo navalis 461 



heart to the anterior end of the caecal typhlosole. The term caeca! 

 arU ry seems appropriate for this vessel (c. a., pi. 22, figs. 1, 4; pi. 24, 

 fig. 12). After passing through the typhlosole the blood flows into 

 the sinuses in that part of the body. 



Sigerfoos (1908) states that the interior of the caecum in the 

 species he studied is ciliated. None of the present writer's prepara- 

 tions show any cilia whatever in the caecum, nor are the cells of the 

 tall, columnar variety which usually bears cilia. The caecum of a 

 living animal, just removed from the wood, was opened and the con- 

 tents washed out with a pipette. Small quantities of mercuric sulphide 

 and of fine carborundum dust were placed on various parts of the 

 wall and on the typhlosole. There was no indication of any ciliary 

 action, though such activity was very evident in other parts of the 

 stomach and in the pallial cavity under like conditions. Slow writh- 

 ing movements of the typhlosole were observed, however, and it is 

 apparent that material is moved in and out of the caecum by muscular 

 movements of the walls rather than by cilia. The experiment was 

 repeated on several animals with similar results. This muscular 

 movement approaching peristalsis is an unusual development in this 

 order of lamellibranchs. 



The orifice between the caecum and the stomach (c. o., pi. 22, 

 figs. 1, 4; pi. 23, figs. 6, 7; pi. 24, fig. 12) is incompletely divided into 

 two openings by two lateral infoldings of the wall. The right fold 

 is continuous with the caecal typhlosole. This arrangement probably 

 provides for simultaneous ingress and egress of wood chips through 

 the two divisions thus formed. The musculature of this orifice has 

 not been worked out. 



Deshayes (1845-1848) and Quatrefages (1849) describe a caecum 

 strikingly different from that described here and by other authors. 

 Deshayes calls it the second stomach. It is thin walled, with a narrow 

 orifice, and with a typhlosole ("valvule") like a funnel. This second 

 stomach doubles back on itself and ends blindly. It is buried in brown 

 hepatic tissue. The intestine takes off from it. Quatrefages goes into 

 less detail in describing his species but his figures indicate essentially 

 the same structure. He denies, however, that the intestine leaves the 

 caecum and believes this statement to be an error on the part of 

 Deshayes. 



The sac of the crystalline style (= caecum, Nelson, 1918) (s. c. s., 

 pi. 22, fig. 1; pi. 23, figs. 6, 7, 8) lies in a transverse position in the 

 lower part of the foot, opening into the stomach on the left. The 



