14° ' BULLETIN OF THE BUREAU OF FISHERIES. 



trom the comers of which two pairs of triangular gill-like folds extend backward. These 

 are the labial palps. 



The labial palps arise as a prolongation of the lips on both sides of the mouth, form- 

 ing a two-paired organ which is so situated that the upper pair lie externally to the lower 

 pair when they are in normal position. They are therefore distinguished as outer and 

 inner labial palps (fig. nS, OLP and ILP). The angle which is formed between the 

 palps at their point of origin on each side marks the anterior termination of the gills and 

 the position of the pigmented eye spots. In form the palps are long, smooth, triangular 

 bands marked on the median side with transverse ridges which extend from the middle 

 to the ventral edge of each palp. A single longitudinal ridge runs from the corner of the 

 mouth to the tip of each palp and forms the line of demarcation between the smooth and 

 ridged side (fig. 1 19). The inner palps are much broader at the base than are the outer 

 ones and are continuous with the lower lip on their ridged side, while the smooth side is 

 attached to the surface of the liver. The outer palps are continuous with the upper lips on 

 their ridged side and attached to the inner wall of the mantle with the opposite side. 



The oesophagus arises directly at the mouth opening and continues backward and 

 upward, bending off slightly to the right of the median plane to enter the anterior end 

 of the stomach. 



The stomach is a small sac of irreguiar form, usually more or less elliptical, with 

 small pockets sometimes present in the dorsal, lateral, or ventral walls. It is situated 

 dorsally just below the middle region of the hinge ligament and lies chiefly on the right 

 side of the body, completely surrounded by liver tissue (fig. 120, St). The ventral stomach 

 diverticulum described by Sabatier (1877) was not found to be regularly present. 



Numerous large canals open into the stomach from the liver. In Mytilus gallopro- 

 vincialis List (1902) generally found 13 in all, 6 emptying in on the right ventral side, 4 

 on the left ventral side, 1 on the left wall, and 2 on the left dorsal wall. Sabatier states 

 for Mytilus edulis that a number of gland canals empty into the stomach, without giving 

 the number. Purdie (1887) says that in Mytilus latus the vessels empty into the under 

 half of the stomach. In the author's observations there could be found no definite num- 

 ber nor regular arrangement to the liver canals. In number they varied from 8 to 14. 

 A majority of these might open on either the right or left side or on the floor of the 

 stomach. 



The direct intestine arises from the posterior end of the stomach and passes back- 

 ward almost on the mid line except in its posterior third, where it bends slightly to the 

 left side and terminates in a blind sac or ccecum of the crystalline style on the dorsal sur- 

 face of the posterior adductor muscle (fig. 120, DI and Coe, p. 141). When the animal is 

 well nourished the direct intestine is almost filled with a transparent, gelatinous rod 

 which extends its whole length from the stomach to the ccecum. 



The recurrent intestine arises from the median side of the direct intestine at the 

 point where it crosses the mid-dorsal region of the posterior adductor muscle. It runs 

 transversely for a short distance to the right side of the animal and then turns directly 

 forward to run parallel with the direct intestine as far as the posterior end of the stomach ; 

 at this point it bends gradually to the left, passing over the direct intestine and then 

 downward and forward over the left side of the stomach almost to its anterior end, where 

 the intestine suddenly makes a posterior loop. This bend marks the beginning of the 

 terminal intestine. 



