CLAM FISHERY OF PASSAMAQUODDY BAY 



23 



SESSIONAL PAPER No. 22a 



into the cavity above. The outer lamella of each outer gill is united above with the 

 mantle, the inner lamella of the outer gill and the outer lamella of the inner gill are 

 continuous, the inner lamellae of the inner gills unite for a distance posteriorly and then 

 they diverge round the upper part of the visceral mass to which they become united 

 except for a space above the centre of the abdomen where there is a branchial cleft. 



Labial Palps. — Between the anterior ends of the gills and the anterior adductor 

 muscle are, on each side, a couple of small flaps termed labial palpi, looking much like 

 miniature gills. They constitute an anterior and a posterior pair, the right and left 

 palp of each pair being grown together at their bases, across the front of the abdomen. 

 It is between the transverse balconies thus formed that the mouth is situated. 



Supra-branchial or Cloacal Chamber. — To inquire further into the inner organiza- 

 tion of the clam it will be of advantage to remove entirely the left half of the mantle 

 and of the siphons together with the two gills of the left side. This will expose, lying 

 above the posterior part of the large branchial chamber, a much smaller supra-branchial 

 or cloacal chamber, continued posteriorly into the dorsal or anal siphon. The transverse 

 partition, separating the cavities of the siphons, extends forwards as the line of union 

 of the gills on to the dorsal part of the abdominal mass. Looking down upon that part , 

 of it which forms the floor of the supra-branchial chamber, one can see the four longi- 

 tudinal rows of openings of the water-tubes from the gills. Curving over the posterior 

 adductor muscle will be found the rectum or terminal portion of the intestine, which 

 discharges by means of its anal opening into the cloacal chamber. Farther forwards, on 

 the dorsal walls of the abdominal mass, are the small openings of the excretory and repro- 

 ductive organs. Thus the water which has passed through the gills, the undigested 

 matters from the intestine, the fluid excreta from the renal organs, and the genital pro- 

 ducts, are all thrown into the cloacal chamber and are swept by an exhalent current 

 through the dorsal siphon to the outside. (Fig. 5.) 



Digestive System. — The terminal openings of the intestinal canal have been already 

 noticed ; between these two points it has the form of a much coiled tube moso of which 

 lies in the abdominal mass. By dissecting off the left wall of the abdomen and care- 

 fully picking away parts of its contents the course of the intestine may be followed. 

 The mouth lies on the anterior end of the visceral mass, behind the anterior adductor 

 muscle and some way above the base of the foot. It is guarded by two pairs of 

 labial palps or oral lobes, which are of importance in directing the food matters brought 

 into the branchial chamber towards the mouth. The bases of the upper ones unite 

 above the mouth forming an upper lip, and the lower ones in a like manner form a lower 

 lip. The short a^sophagus expands into a somewhat capacious stomach, which in the 

 dead clam is usually empty and its walls thrown into folds. Surrounding the stomach 

 is a lobulated, greenish or brownish coloured digestive gland or liver, whose secretion is 

 poured into the stomach to aid digestion. From the stomach food passes into the intes- 

 tine, which in fresh specimens is usually distended and dark coloured from its contents. 

 The intestine bends alternately forwards and backwards as well as from side to side, 

 making some half dozen folds while it passes downwards in the abdomen, it then runs 

 backwards to near the posterior limit of the abdomen, turns upwards and forwards, and 

 leaves the abdominal mass in the middle of its dorsal surface. Here it bends backwards 

 and enters the pericardium, the cavity of which it traverses in the median sagittal 

 plane of the body. This dorsal, posterior portion of the intestinal tract, known as the 

 rectum, then runs over the posterior adductor muscle and opens by the anus into the 

 cloacal chamber. From the posterior end of the stomach springs a diverticulum which 

 contains a peculiar gelatinous rod called the crystalline style ; very large in this 

 species, curving round near the posterior and ventral surfaces of the abdomen to end at 

 the base of the foot. 



Reproductive Organs. — Filling a great part of the abdomen, and especially between 

 the folds of the intestine, is the pale, yellowish genital gland — ovary in the female, 

 testis in the male. (Plate I V., Fig. 5, G.G.) It opens by a pore on each side of the 

 roof of the abdominal mass into the cloacal chamber above. 



Excretory System. — Situated under the pericardium and in front of the posterior 

 adductor muscle is the renal organ, kidney or organ of Bojanus. It is composed of right 

 and left nephridia, each of which is a tube folded once upon itself with both ends turned 



