232 OILMAN A. DREW. 



sinuses. Most of the blood from all of these organs is distributed 

 to the kidneys through systems of capillary spaces. The branch- 

 ing of these vessels is not conspicuous on the surface of the kid- 

 neys, but is better seen by cutting the kidneys open. That not all 

 of the blood necessarily traverses the capillary spaces of the kid- 

 neys is indicated by the fact that injections of the systemic veins 

 frequently fill the veins that carry the blood away from the kid- 

 neys as well as those leading to it. This is much more frequently- 

 the case when injecting from the posterior surface of the adductor 

 muscle than when injecting from other places, and seems to be 

 dependent upon a direct connection between the vessel in ques- 

 tion and the sinuses on the antero-ventral surface of the adductor 

 muscle near the dorsal ends of the kidneys. 



Of the blood that leaves the heart, only that which goes to 

 the mantle remains to be accounted for. This is collected and 

 returned directly to the heart (Fig. 5, pv.} 



All of the blood that leaves the kidneys is conducted to the 

 gills. The blood from each kidney is collected into a sinus that 

 runs along the border of the kidney that is applied to the adductor 

 muscle. This sinus, which also seems to receive blood from the 

 sinuses on the anterior and ventral surfaces of the adductor muscle, 

 bends abruptly ventrally over the anterior end of the kidney and 

 is continued on the lower border of the suspensory membrane of 

 the gill (Fig. I, ba) to the posterior end of the gill, supplying 

 the gill with branches throughout its length. 



Blood vessels leave the vessel that carries blood from the 

 kidney, opposite each of the inter-lamellar junctions of each of 

 the gills supported by the suspensory membrane. Each of these 

 branches is continued along the free border of the membrane 

 that forms the inter-lamellar junction (Fig. 7, ba') until it reaches 

 the free edge of the lamella, the edge that is not attached to the 

 suspensory membrane. That, is, if the branch supplies an outer 

 gill, it leaves the suspensory membrane along the free border of 

 an inter-lamellar junction and crosses over to the free border of 

 the outer lamella of this gill. Here the vessel is continued 

 down the enlarged, modified filament that is concerned in the 

 formation of the inter-lamellar junction (Fig. 7, ba"} giving out 

 side branches through each of the inter-filamentar junctions 



