CLAM FISHERY OF PASSAMAQUODDY BAY 



21 



SESSIONAL PAPER No. 22a 



Siphons. — The siphons, or funnels, are two muscular tubes bound together as one 

 long, thick, fleshy mass, projecting from the posterior end of the animal between the 

 gaping valves. One tube is placed dorsal to the other so that their combined depth is 

 greater than their breadth, while their length depends upon the size of the animal and 

 its condition of extension or retraction. In a medium-sized clam the siphons may reach 

 four to six inches in length. At the outer end each siphonal tube is supplied with a 

 number of stout fimbriae, or feeling hairs, that, besides receiving sensations of disturb- 

 ance that may cause the withdrawal of the siphons, may also close the openings 

 and prevent large particles of solid matter from entering. If, while a clam is 

 lying with its siphons out, particles of carmine are dropped into the water above, it 

 can be determined that there is a current of water entering the lower, larger opening, 

 but that the carmine is repelled from the upper opening. It is through the lower of 

 these siphons that the animal receives its supply oE sea water, that, besides serving the 

 purposes of respiration, also conveys the food matters upon which it lives. It must be 

 borne in mind, however, that the mouth is at the opposite end of the body from the 

 siphons, which latter are often called the 'neck,' or the ' head,' by fishermen and others, 

 who distinguish different species by such expressions as ' the little necked clam,' &c. 

 And, indeed, the long, extended, siphonal mass, with its blackened, cuticularized outer 

 end, may well give rise to such an impression. Tracing the lower wall of the siphons 

 forward it is found to stretch like a curtain between the vertical edges of the valves. 

 This is a portion of the mantle, and is continuous round the front end of the clam, 

 where, however, there is a vertical slit through which may be protruded the slender, 

 soft, fleshy foot. Both mantle and foot can be better described later. 



INTERNAL ORGANIZATION. Plate III, Figs. 3, 4 ; Plate V, Fig. 5. 



When a clam is disturbed it of course contracts, closing its shell and holding it closed 

 with great muscular strength. In order to learn its internal structure it is necessary to 

 remove one of the valves. Insert the blade of a knife at the posterior end and draw it 

 forward close against the left valve. If the knife is carried round the anterior end 

 both of the stout muscles that draw the valves together will be severed. The left valve 

 may then be lifted up and broken loose at the hinge. There will now be exposed, on 

 the one side, the inner nacreous surface of the shell already mentioned, with a number 

 of lines and marks to be further noticed ; and, on the other side, the fleshy mantle, 

 with several organs either exposed or shining through. (Fig. 3.) 



As the two halves of the shell were seen to differ somewhat on the outside, so there 

 a.re also differences on the inside ; of these the chief difference is the presence, in the 

 middle of the hinge margin of the left valve, of a strong, broad, cardinal tooth, project- 

 ing perpendicularly inwards. Between its outer, upper surface and the overlapping 

 portion of the umbo of the right valve is the hinge ligament, an elastic, horny substance 

 which occasions the divergence of the valves when the muscles are relaxed. Near the 

 anterior end of the valve is the mark of attachment of the severed anterior adductor 

 muscle, and half way between the tooth and the posterior end is the posterior adductor 

 muscle, while extending from one to the other ventral wards is the pallial line, indicating 

 the seam along which the mantle was held by the pallial muscles against the shell. Below 

 the posterior adductor muscle the pallial line has a broad, deep indentation with its con- 

 cavity looking backwards. This marks the position of attachment of the retractor 

 muscle of the siphons. 



Turning to the soft parts exposed, we shall be able to recognize the large 

 anterior and posterior adductor muscles of the foot, whose fibres run across from 

 one shell to the other. Behind the ends of the anterior adductor are the much 

 smaller anterior retractor muscles of the foot, whose fibres pass down the front end of 

 the abdominal mass to be inserted intp the base of the foot. Just in front of the pos- 

 terior adductor are to be seen the posterior retractor muscles of the foot. They con- 

 verge from opposite sides, running inwards, forwards and downwards, to unite and join 

 the upper posterior part of the visceral mass, over the sides of which their fibres spread. 

 Below the posterior adductor muscle are the paired retractor muscles of the siphons, 



