coe: nemerteans of west and northavest coasts. 39 



C. Bdellonemertea — In this order the proboscis is similar in 

 general structure to that of the Hoploneniertea, although a stylet 

 apparatus is not present. There is, however, a bulb-like expansion 

 near the posterior end of the organ, between the glandular chamber 

 and the retractor muscle. This bulb is thought to represent a rudi- 

 mentary condition of the middle chamber and stylet apparatus of 

 the Hoplonemertea. 



Blood Vascular System. 



A. Paleonemertea. — The simplest type of circulatory system 

 occurs in Cephalotiirix, where the blood circulates in two main 

 longitudinal lateral vessels, without branches, united at the anterior 

 and posterior ends of the body. These are situated in the body 

 parenchyma beside and somewhat beneath the alimentary canal. 

 In Carij^ella the lateral vessels unite to form large communicating 

 lacunae in the head. In many species there is a single very large 

 cephalic laciina, more or less interrupted and broken up into 

 smaller chambers by fibrous partitions, and these lacunae surround 

 the rhynchodaeum on all sides. There is also a pair of rhynchocoel 

 vessels which originate from the lateral vessels in the mouth region 

 then pierce the wall of the proboscis sheath and extend backward 

 for some distance in the cavity of the rhynchocoel, where they 

 appear as ridges in the ventro-lateral walls of the sheath. They 

 exhibit numerous regularly arranged communications with the lat- 

 eral vessels which they conmionly join a little anterior to the 

 nephridial region. A pair of small esophageal vessels is sometimes 

 found in this genus, and in C. alhocincta the lateral vessels send off 

 numerous anastomosing branches about the esophagus. 



In Carinomella, as in Carinella, there are large anastomosing 

 blood lacunae in the head (PI. 6, fig. 53) and a single pair of lateral 

 vessels (PL 7, figs. 55, 56) which send outgrowths into the proboscis 

 sheath. The lateral vessels are large and thin w^alled in the eso- 

 phageal region and lie internal to the inner circular muscular layer 

 (PI. 6, fig. 54), but pass outside this muscle anterior to the nephridial 

 region (PI. 7, figs. 55, 5b), very much as in Carinella linearis. 

 Shortly behind the nephridial region the lateral vessels acquire 

 muscular walls and are strongly contracted at intervals. In the 

 intestinal region (PL 9, fig. 59) they lie beside the intestine and 

 beneath the sexual glands. 



