MOLGULA 137 



appear as light-colored bands in the pharyngeal wall. Find 

 and trace a white or cream-colored line extending in the mid- 

 ventral line from the base of the incurrent siphon to the opposite 

 side of the body. This is the endostyle; it is a ciliated and 

 glandular groove which lies between two folds in the mid- 

 ventral wall of the pharynx; it extends the length of that 

 structure and ends posteriorly near the opening of the pharynx 

 into the oesophagus. Find this point. The oesophagus is short 

 and communicates with the stomach, and these two divisions 

 form the lower and thicker limb of the S-shaped digestive 

 tract. The upper limb is formed by the intestine, which passes 

 to the base of the excurrent siphon, where it ends with the 

 anus. Find these organs. 



The reproductive system. Molgula is hermaphroditic. The 

 sexual organs consist of a pair of large hermaphroditic glands, one 

 of which is seen on each of the lateral sides of the body. 

 A short duct runs from each gland to the base of the excurrent 

 siphon. On the left side the duct will be seen alongside the 

 posterior end of the intestine ; find it. 



The circulatory system. On the right side of the body beneath 

 the hermaphroditic gland will be seen the heart in its pericardium. 

 It is a muscular sac from each end of which proceeds a large 

 blood vessel. The vessel leaving the ventral end (at the 

 observer's right) is called the cardio-branchial vessel; it passes 

 along the mid-ventral side of the pharynx, beneath (external to) 

 the endostyle, and gives off branches which run transversely 

 along the pharyngeal wall. The vessel leaving the dorsal end of 

 the heart is called the cardio-visceral ; it breaks up into numerous 

 branches, which ramify among the viscera and other parts of 

 the body. From the viscera the blood is collected again in 

 a vessel called the viscero-branchial, which passes along the mid- 

 dorsal pharyngeal wall and gives off transverse branches. 



The heart of tunicates is peculiar in that its pulsations 

 change the direction of the flow of the blood alternately from 



