ARENICOLA 105 



followed by an esophagus which extends through several seg- 

 ments. At the junction of esophagus and stomach note the 

 two conical, yellowish esophageal glands. The stomach is 

 covered with a vascular gastric plexus between the branches 

 of which is the yellow chlorogogue tissue. When you have 

 finished all dissection, observation and drawing, slit open the 

 alimentary canal and locate the ventral ciliated groove. 



Vascular System. — There is a closed blood system. The 

 general course of the circulation is anteriorly in the dorsal 

 and longitudinal intestinal vessels and posteriorly in the ven- 

 tral vessel. The principal vessels are: 



1. Dorsal Blood Vessel. — Arises near anus, extends along 

 dorsal side of intestine and terminates in small vessels on 

 esophagus. It communicate with the following: 



(a) Intestinal Vessels. — One pair in each posterior seg- 

 ment, more numerous on anterior part of intestine. 



(b) Efferent Branchial Vessels. — From last seven pairs of 

 gills. 



(c) Gastric Plexus. — Numerous vessels over wall of 

 stomach. 



(d) Nephridial Vessels. — To first three nephridia. 



(e) Esophageal Pouch Vessel. 



(/) Septal Vessels. — To second and third septa. 



2. Ventral Blood Vessel. — Arises by fusion of small ves- 

 sels at anterior end of body. It communicates with the fol- 

 lowing: 



(a) Septal Vessels. — From the first three septa and the 

 diaphragmatic pouches. Branches of second and third septal 

 vessels connect with the neural vessels (see p. 106). There 

 is also a connection between ventral and each neural at level 

 of second setigerous sac. 



(b) Segmental Vessels. — One pair per segment, associated 

 with the setigerous sacs and with the nephridia and gills 

 where the two latter are present. 



(c) Intestinal Vessels. — To intestinal wall. 



3. Subintestinal Vessels. — A pair running most of the 



