178 Practical Zoology. 



How strongly can it hold to the surface it is on ? Watch the 

 actions of the tube feet through the glass. Will it climb on 

 a slender support, such as a cane, or large glass tube ? Can 

 you learn about its food and mode of eating? Try to get 

 answers to the questions asked above as to the live starfish 

 at home. Do you find any evidences as to the mode of develop- 

 ment and growth of starfishes ? Do the adults have any care of 

 the young ? Do starfishes do any good ? Have they economic 

 importance ? Do they do any harm ? How can their ravages 

 be checked ? 



EXTERNAL FEATURES OF THE STARFISH. 



For this work there is needed : 



1. A set of dried specimens, one for each student ; such a set 

 may be used with successive classes and will last for years if 

 carefully handled and kept in a dry place. 



2. Alcoholic specimens for dissection. 



3. It is desirable to have a set of prepared slides, showing 

 cross sections of a decalcified ray of a young starfish, and a 

 ground-down section of a calcareous plate, etc. 



4. An injected starfish and a number of injected rays. 



DRIED SPECIMEN. 



1. Observe, first, the shape of the body as a whole. The 

 central portion is the disk, and its radiating extensions are the 

 arms, or rays. Note that the rays are bilaterally symmetrical. 



2. The mouth is at the center of a thin membrane in the 

 middle of the oral surface ; the opposite surface is called aboral. 



3. Cut into one of the rays. Observe that the body cavity is 

 bounded by a leathery wall, in which are embedded hard plates. 

 Compare a piece of a ray of an alcoholic specimen with the 

 dried one. 



4. Test the flexibility of the integument of the alcoholic 

 specimen. By picking with forceps, prove that there is soft 

 matter, both on the outside and on the inside of the hard plates. 



