1 64 PHYLUM CHORD ATA 



bars or ridges, which are easily seen and have already been 

 mentioned. Through all these bars the blood circulates, being 

 brought to them either by the cardiobranchial or the viscero- 

 branchial blood vessels, and respiration is thus carried on. 



Lay the animal with the left side uppermost. Slit open the 

 incurrent siphon and the pharynx by inserting the point of fine 

 scissors in the siphon and, after cutting its wall to its base, carry- 

 ing the cut through the wall of the pharynx along the side of and 

 parallel with the midventral line to the posterior end of that 

 organ. Lay the pharynx open. The twelve large longitudinal 

 bars will be seen projecting into the pharyngeal lumen. Trace 

 them throughout their entire extent. Find with the aid of a dis- 

 secting microscope or a hand lens the rows of branched tentacles 

 at the base of the incurrent siphon and count them. 



In the midventral line note the endostyle ; notice also that it 

 is a groove. Trace the endostyle forward to the base of the siphon. 

 At its anterior end the endostyle is continuous with a ciliated 

 ridge which encircles the anterior end of the pharynx and is called 

 the peripharyngeal ridge. This ridge is itself continuous on the 

 dorsal side of the animal, that is, on the side opposite to the endo- 

 style, with a ciliated longitudinal ridge called the dorsal lamina, 

 which passes along the mid-dorsal line to the opening of the 

 oesophagus at the posterior end of the pharynx. Trace the peri- 

 pharyngeal ridge and the dorsal lamina. 



These organs aid in the ingestion of the animal's food. The 

 endostyle is a glandular and ciliated groove; the gland cells 

 secrete a viscid substance which catches the food particles ; the 

 cilia create a current which drives them toward the anterior 

 end. Here they meet a current created by the cilia of the peri- 

 pharyngeal ridges which takes them around the pharyngeal wall 

 to the dorsal lamina, along which they are driven posteriorly to 

 the opening of the oesophagus. 



Between the siphons note the ganglion and subneural gland. 



Exercise 5. Make a semidiagrammatic drawing showing the struc- 

 tures which appear in connection with the pharyngeal wall. 



Exercise 6. Make a large diagram of Molgula and show the relative 

 positions of the different organs ; label all. 



