234 CHORDATA 



gion, is normally maintained in a vertical position. The 

 posterior end is also kept upright, and can be moved up and 

 down in a vertical shaft opening on the surface, thus en- 

 abling the animal to eject the residue of sand from the anus. 

 For the internal anatomy, the account in the Cambridge 

 Natural History may be consulted. Important chordate 

 characters are the notochord, the dorsal central nervous sys- 

 tem, and the branchial clefts. 



Agassiz: The History of Balanoglossus and Tornaria. Amer. Acad. 



Arts and Sci., 9, 1873. 

 Bateson: The Early Stages of Balanoglossus. Quart. Jour. Mic. Sci., 



24, 1884. 

 : The Late Stages of the Development of Balanoglossus. Quart. 



Jour. Mic. Sci., 25, 1885. 

 Morgan: The Growth and Metamorphosis of Tomaria. Jour. Morph., 



5, 1891. 



■ : The Development of Balanoglossus. Jour. Morph., 9, 1894. 



Ritter and Davis: Studies on the Ecology, Morphology and Speciology 



of the Young of Some Enteropneusta of Western North America. 



Univ. Calif. Pub. Zool., 1, 1904. 



UROCHORDA 



MOLGULA MANHATTENSIS 



Specimens of this simple ascidian may be found attached 

 to old piles, associated with many other forms. In some 

 localities they may be so abundant as practically to incrust 

 the piles, and crowd each other out of shape. Examine such 

 a mass and see how different sized individuals are associated. 

 Pull them apart and see if there is any tissue connection be- 

 tween them that would indicate a definite relation between 

 neighbors. Do you understand how the individuals get 

 started in the places where they are attached? With a glass- 

 bottomed pail you can see the expanded individuals on the 

 piles, but they can be more satisfactorily studied in small 

 dishes of sea water. 



1. Observe the contraction and closure of the two siphons 

 when the animal is irritated. 



2. Add a little powdered carmine to the water to deter- 

 mine which is the incurrent or oral and which is the excur- 

 rent or atrial siphon. 



