BDELLOURA OR SYNCCELIDIUM. 49 



memoranda, if necessary, of the shapes of the various pieces. 

 Carefully cover the dish and set it away. Examine the pieces 

 with a hand-lens every twenty-four hours 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 maculata. 

 Arch. f. Entwickelungsmech.j 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 external 

 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 pigment, they 

 are very favorable for the study of internal structure, and may 

 be used to demonstrate the structures not observed in Planaria 

 maculata. 



1. Observe the movements of the living worms in a watch- 

 glass 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 (triclad 

 type) and many secondary diverticula is easily recognizable. 

 The mouth can sometimes be made out as a small circular open- 

 ing leading ventrall}^ 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. Ex- 

 amine the specimen by reflected light, looking particularly at 



