BOTRYLLUS. 169 



3. Study the stolon with its flattened epicardiac tube. This 

 tube is derived from the branchial sac and is accordingly endo- 

 dermic. 



4. Study buds of various sizes and see how the inner vesicles 

 arise from the epicardiac tube. 



5. Try to make out the entire course of the circulation of the 

 blood. Notice especially the heart, branchial vessels, vessels of 

 the mantle, and the circulation of the stolon. Watch the pulsa- 

 tions of the heart and see the reversal of the blood-current. Is 

 the heart-beat synchronous in different individuals? What part 

 of the blood is colored? 



6. Study the action of the cilia in the gill clefts. 

 Drawings of a colony and of an individual are desirable. 



BOTRYLLUS. 



The small, radially arranged colonies of this composite ascidian 

 are common on eel-grass, from which they may be separated by 

 means of a knife, and studied alive in a watch-glass with a low 

 power of the microscope. The cleaner and more transparent 

 colonies should be selected. 



1. Note the character which makes the form a " composite" 

 ascidian the common tunic or test. Find the mouths and the 

 common cloacal cavity. Would it be correct to say that a common 

 atrium is present? 



2. Find the annular blood-vessel and its numerous ampullce. 

 Do you observe any striking facts regarding the circulation? 

 What function have the ampulla? 



3. With your knowledge of Molgula as a guide, identify as 

 many of the organs as possible. (This is sometimes difficult 

 because of pigment.) 



4. Very young colonies, with only the first one or two genera- 

 tions of buds, may also be found on eel-grass, appearing as trans- 

 parent hemispherical lumps about a millimeter in diameter. 

 These should be fixed and stained on the eel-grass, and later 

 mounted (either still attached or removed) in balsam. These 

 will show very clearly the formation of buds of the "parietal" 



