412 APPENDIX. 



of a colony. Microscopic examination will show the fleshy part 

 of the colony to be protected by a transparent covering. Each 

 nutritive zooid will be found to have a circle of tentacles sur- 

 rounding the mouth which leads to the digestive cavity, the 

 lower end of the latter being continued into a fleshy tube which 

 runs to the tube traversing the main stem. The cell-layers are 

 usually well defined. The reproductive zooids are without ten- 

 tacles, and will probably contain young in various stages of de- 

 velopment. 



If Sea-anemones (Figs. 38, 199) can be obtained their struct- 

 ure and habits should be studied and compared with those of 

 the hydra and the hydroids. Alcoholic specimens are most 

 satisfactorily studied by making both transverse and longitudi- 

 nal sections about a fourth of an inch in thickness. Float the 

 sections in dishes of fifty per cent, alcohol (Fig. 198). 



ECHINODERMS. As representatives of these the Starfish, 

 Sea-urchin, and Sea-cucumber are useful. They may be studied 

 in the fresh condition or preserved in alcohol. After examin- 

 ing the shape and the external features of the body, as spines, 

 ambulacral grooves and areas, ambulacral feet, mouth, eyes, 

 etc. (Fig. 212), the body may be opened, in the case of the 

 Starfish and Sea-cucumber, by slitting with a knife or scissors, 

 and the internal organs examined. Cut some of the rays of 

 the Starfish crosswise ; from others remove the top. The di- 

 gestive system in the Starfish consists mainly of a short oesoph- 

 agus leading to a set of five wrinkled pouches, at whose outer 

 ends will be found band -like retractor and protractor muscles, 

 the pouches forming the cardiac portion of the stomach, which 

 is farther continued into a pentagonal sac, at whose corners enter 

 ducts from the lobes of the " liver" or hepatic coeca, the latter 

 being attached to the roof of the ray by a mesentery (Fig. 126). 

 At the point of union of two adjacent rays will be found the 

 grape-like clusters of sexual glands. On each side of the mid- 

 dle line vertebral ridge of the ray will be seen rows of 

 water-sacs or ampullae, each of which supplies an ambulacral 

 foot. Other sacs will be found surrounding the mouth. 



The Sea-cucumber differs in several respects from the Starfish 

 as regards internal structure. The digestive system consists 

 mainly of a long tube, bent once or twice upon itself, at the 

 Jower end of which is attached the much branched respiratory 

 tree. Longitudinal muscles run from near the base of the ten- 



