VASCULAR SYSTEM. GONADS. 



continuous with the heart. The proboscis portion of this vessel 

 is called the afferent vessel of the proboscis. It runs in the dorsal 

 mesentery, or in what remains of it, in the trunk, while in the 

 collar it is placed between the two perihaemal cavities (Fig. 69). 

 In the proboscis it runs between the notochord and the hind 

 end of the pericardium where it is enlarged to form the heart 

 (Figs. 60, 65). (2) A ventral longitudinal vessel extending 

 through the whole trunk and into the hinder part of the collar 

 (Fig. 69). It runs in the ventral mesentery or in what remains 

 of it. In the collar the ventral vessel divides and becomes con- 

 tinuous with the two plexuses of vessels which are contained 

 in the vascular folds already described. These pass in front 

 into the efferent vessels of the proboscis (Fig. 67 rev) which run, 

 one on each side, through the chondroid tissue in the neck of 

 the proboscis to the hind end of the glomerulus, with the blood 

 spaces of which they are continuous. There is in all the basement 

 membranes a capillary network by means of which these main 

 vessels are connected. This network is principally developed in 

 the body wall, in the gut wall, particularly in the hepatic region, 

 and in the gonads. That part of this network which lies in the 

 pharynx wall and is presumably of importance in respiration is 

 of course directly connected with the dorsal vessel. The dorsal 

 vessel is supposed to be contractile and its contractions prob- 

 ably travel forwards, so that the blood passes from it to the 

 heart. From the heart it passes, driven by the contraction of 

 the transverse muscle in the ventral wall of the pericardium, to 

 the spaces within the folds of the glomerulus. Thence it passes 

 into the efferent vessels of the proboscis which are continued 

 from the hind end of the glomerulus through the chondroid 

 tissue into the vessels of the vascular folds and so into the ventral 

 trunk vessel. 



There are other main vessels in addition to the two mentioned : e.g., in 

 Ptychodera there is on each side in the lateral septa a vessel which arises 

 in the skin in front and enters the intestinal plexus behind ; it supplies the 

 i:i>ii,ids. There are also definite main vessels both in the tongue and prim- 

 ary bars of the pharynx, supplying the capillary network. 



The reproductive organs. The sexes are separate and the 

 reproductive organs are similar in form and arrangement in the 

 two sexes. They are simple or branched sacs which project into 

 the coelom and are placed in the lateral part of the trunk in the 



