BDELLOURA OR SYNCCELIDIUM. 37 



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. If the water in the dish begins to show signs of becom- 

 ing foul, transfer the pieces to a clean dish of fresh pond-water. 

 Do not use water from the tap. 



BDELLOURA OR SYNCOELIDIUM. 



Most triclads are free-living, but a few are ectoparasites. 

 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 struc- 

 tures 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 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. Ex- 

 amine 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- 

 vascular tuhules. The region anterior to the cerebral ganglia 

 is a favorable place. They form a clear, branching tracery, a 



