68 PLATYHELMINTHES 



for the next week or ten days. Change the water in the dish 

 at least twice a week. Do not use water from the tap. 



Curtis: The Life History, the Normal Fission, and the Reproductive 

 Organs of Planaria maculata. Proc. Bost. Soc. Nat. Hist., 30, 1902. 



Morgan: Experimental Studies of the Regeneration of Planaria macu- 

 lata. Arch. f. Entwickelungsmech., 7, 1898. 



Parker and Burnett: The Reactions of Planarians With and Without 

 Eyes to Light. Am. Jour. Physiol., 4, 1900. 



BDELLOURA OR SYNCOELIDIUM 



Most triclads are free-living, but a few live on the ex- 

 ternal surfaces of other animals. The above-mentioned forms 

 are found upon the proximal joints of the walking legs and 

 in the gill books of Limulus. Owing to the absence of pig- 

 ment, they are very favorable for the study of internal struc- 

 ture, and may be used to demonstrate the structures not ob- 

 served in Planaria maculata. 



1. Observe the movements of the living worms in a 

 watchglass of sea water; then place a specimen on a slide, 

 dorsal side uppermost, and cover with a slip. 



If any of the points of structure mentioned for Planaria 

 have not been observed, try to find them on this form. 



2. Notice that the gut with its three main branches (tri- 

 clad type) and many secondary diverticula is easily recog- 

 nizable. The mouth can sometimes be made out as a small 

 circular opening leading ventrally from the posterior end of 

 the pharyngeal sheath. 



Compress the specimen as much as possible by drawing 

 off the water with filter paper and look for: 



3. The cerebral ganglia, a bilobed structure beneath the 

 eye spots, that appears as a slightly lighter area. 



4. From the cerebral ganglia two longitudinal nerve cords 

 pass backward, and several smaller nerves pass off in front. 

 Examine the specimen by reflected light, looking particularly 

 at the nervous system and pharynx. What relation have the 

 nerve cords behind? 



5. With the high power and good light, look for the water- 



