JOXJENAL OF ENTOMOLOGY AND ZOOLOGY 91 



It communicates with the main body cavity at a point on either 

 side just anterior to the rhinopliores (G), and with the pedal 

 sinus complex at numerous points (H), the main ones being at 

 the head and tail, and just anterior and posterior to the opening 

 into the auricle. It also gives off many short and long branches, 

 above and below, as well as branches to the papillae. 



The aeration of this blood is undoubtedly accomplished 

 through the skin of the back and sides, to which branches of the 

 sinuses are closely applied and through the pajnllse, which seem 

 especially adapted for this purpose. The sinuses in the papillae 

 are much dilated at the ends, and communicate by many fine 

 branches with the spongy network of which the substance of the 

 papilla? is composed, so that the blood is brought in close contact 

 with the epithelium covering the surface. Also, when the animal 

 is alive, the papillae are in constant slow motion, which would 

 facilitate aeration of the blood. 



The lateral sinus opens directly into the auricle by short 

 branches, and the blood is then immediately returned into circu- 

 lation without passing through the branchiae. The blood from 

 the posterior aorta follows a different course from the rest. 

 After passing through a complex mass of sinuses between the 

 liver lobes, it is collected in venous channels that come together 

 in a great sinus running along just above the stomach, from 

 which it is carried to the branehia' by the hepatic vein (A). This 

 gives a single vein to each branchial plume. These run up the 

 posterior side of the main trunk of the plumes and send off 

 branches which, running forward close under the epithelium, 

 are collected in veins (C) which run down the anterior trunk 

 of each plume. These veins are collected into a single one which 

 opens almost immediately into the auricle, thus returning the 

 branchial blood to the circulation, where it is mixed with blood 

 from the lateral sinuses. 



The branchife usually consist of three plumes, but there may 

 be five, the numlier which MacFarland has described as tj-pical. 

 These have a muscular central stalk with several branches, which 

 rebranch into fine ultimate endings. I^ach branchial plume 

 receives a large nerve from the branchial plexus, and a branch 



