MACROBDELLA, PHASCOLOSOMA 119 



the median line. These are joined to the supra-esophageal 

 ganglia. 



Draw the nervous system. 



Open the buccal cavity by cutting along one side and 

 notice the three large buccal muscles, one dorsal and two 

 lateral. These bear many minute denticles that may be seen, 

 in the right position, with a compound microscope. It is by 

 means of these that the leech makes its wound. 



GEPHYREA 

 PHASCOLOSOMA 



This form is commonly found buried in sand between 

 tide marks. Specimens sometimes occur on the same flats 

 with Nereis, but they are generally more abundant where the 

 mud is of a slightly different, more sticky character. 



1. Handle a living specimen and see how turgid it is. If 

 you touch a specimen that has been allowed to expand in a 

 dish of sea water you will find it is rather soft, but becomes 

 turgid upon being touched. How is this accomplished? 



2. Examine a living animal in a dish of sea water. The 

 anterior portion of the body, the introvert, is drawn in, but 

 may occasionally be extended, when it will be seen to bear 

 at the anterior extremity a crescentic crown of tentacles, 

 which partly surrounds the mouth. 



3. Compare with a preserved specimen which has been 

 killed with the introvert extended. 



Make drawings showing the animal with the introvert 

 protruded and with the introvert concealed. 



4. The anus is located on a dorsal papilla, anterior to the 

 middle of the body. Near the anus a pair of lateral papillae 

 mark the position of the nephridiopores. The coiled intes- 

 tine and brown nephridial tubes can probably be seen through 

 the body wall. Note carefully the character of the integu- 

 ment. Is there any indication of spines, appendages, or eye 

 spots? 



For dissection use both fresh and preserved specimens. 



