14 A MANUAL OF .ZOOLOGY 



ing strands. Note the number and extent of each. It will 

 require careful work to demonstrate the short intestine 

 leading from the top of the stomach to the anal opening, in 

 the disk. Look above the stomach for the respiratory tree 

 attached to the disk. Make jjiiawing of the digesUve ap- 

 paratus. In fresh specimens the ovaries are pinkinsh, and 

 the testes are yellowish white; both will be found in the 

 axis 'Of the rays. Settle .whether both appear on the same 

 specimen. Where do they open? 



The hepatic coeca have been removed. Under these 

 and oh either side of the vertebral ridge, the ampul iae or 

 water sacs are found. ' Study injected specimens if pos- 

 sible. Tear ohe open. What is its structure? Press on the 

 ambulacral feet. What effect has this on the ampullae? 

 Are they .connected? 



Now carefully remove all the digestive organs of the 

 -trivium, including the stomach. Notice the stone canal 

 leading down from the madreporic plate. Around the stone 

 canal notice a thin membrane, the pericardium, which con- 

 tains the supposed heart. Before tracing out the stone 

 canal, remove the- peristome and note the following: the 

 circum-oral water tube; the polian, and the racemose vesi- 

 cles. There, is one less racemose • than polian vesicle. 

 Now trace carefully, the stone canal and account for the 

 difference in number of tbe vesicles. Make a_dra'ffiing. of 

 the water vascular system. 



TEe^fespTratpry 'system may be demonstrated^ by show- 

 ing the connection of the tentacles' of the aboral surface 

 with the body, cavity. Small openiijga in the roof of the 

 rays lead to the tube-like tentacles. Study sections to help 

 decide this. 



, Demonstrate the nervous system, .by studying with a 

 hand, lens and also by the use of the microscope. The cir- 

 cum^oral. nerve ring, can be traced throughout in a gross 

 way, .but the radial nerve. will need the microscope and 

 well prepared sections for 4emotiatratioii. 



mYLUM ANNUtATA 



, Lumbricus (Earthworm). 

 Have 'at hand living specimens, as well as specimens 

 prel^erved iii alcohol or formalifl." 'the "tissues in the pre- 

 served apecimens will be harder, and for that' reason are 



