THE STARFISH. 151 



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. 



The above and other desired material for work on ma- 

 rine animals may he obtained of Mr. B. H. Van Vleck, 

 Boston Society of Natural History, Boston, Mass. 



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 bilater- 

 ally 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 im- 

 bedded 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. To show the real nature of the 

 plates and their relation to the integument, proceed 

 as follows : — 



a. Handle a starfish which has been decalcified, i.e. 

 has had its calcareous matter removed by very 

 weak (two per cent) nitric j&eid, chromic or other 



