42 PLATYHELMINTHES. 



2. Observe movements of specimens in a dish of sea-water. 

 Do the suckers have independent movements? 



3. With a low power of the compound microscope, or with 

 a hand-lens, note that the worm is made up of a head portion, 

 the scolex, and of numerous segments, the proglottids. What 

 is the relative size of the proglottids in the different regions of 

 any specimen? Where are new proglottids necessarily pro- 

 duced if the largest are always the oldest? Are the proglottids 

 attached to one another with equal firmness in all parts of the 

 body? Note their peculiar shape, and how they are connected 

 together. In the above examination, if living material is used 

 it will often be desirable to stretch portions of the animal very 

 gently with your forceps. 



4. Note the number and arrangement of the disk-like suck- 

 ers. How are they borne on the scolex? Do you find each 

 sucker to be entirely simple ? 



Draw the adult worm. 



5. Cut from the head-end of a living specimen a piece con- 

 sisting of a scolex and not more than one or two proglottids. 

 Place this on a slide, cover, being careful not to compress too 

 much at first, and examine the scolex carefully again to make 

 sure you understand its structure. 



6. Look for transparent tubes coiling about in the scolex 

 and its suckers. Compress the specimen by drawing off as much 

 water as possible with filter-paper, and look again for the trans- 

 parent tubes. These are portions of the water-vascular system. 

 Recall the description of this system given in the lecture or in 

 text-books. The finer branches which lead from the main trunks 

 are difficult to identify with certainty, but by using the high power 

 of your microscope, and focusing just below the surface in the 

 more transparent portions of the scolex, the flame cells may easily 

 be seen. The " flame " appears like a short, thick whip lost in con- 

 tinual vibration. Find such flames and watch them carefully. If 

 not found at once, lot the preparation stand and examine in about 

 half an hour. In the older preparation they are frequently easier 

 to find. 



