116 THE BIOLOGY OF THE ANIMAL 



ray is closed? How long before you can find 

 evidences that a new raj'' is being formed to re- 

 place the one removed ? Does this new ray ever 

 reach the size of the others ? If so, in how long 

 a time ? How many rays may be removed and 

 still be replaced by new ones ? Do the removed 

 rays ever form a new disk, etc. ? Try handling 

 out of water large starfishes and see if they will 

 voluntarily drop their rays. If so, at what point 

 does the ray become detached ? Is this property 

 of any use to the animal ? 

 Many of the above questions may be decided by a 

 study of a collection of specimens of imperfect and mu- 

 tilated starfishes. 



//. Sexual rejyroduction. 

 a. The structure of the sexual cells. 



1. The spermatozoon. —With a pipette coUeet 

 some of the sperm which a mature male may 

 be found shedding into the water, or remove 

 the testes and with sharp scissors cut them 

 to pieces in a watch-glass of sea- water. Put a 

 drop of the sperm under the high power of the 

 microscope, propping up the cover-glass with 

 bits of wax or paper, and note the spermatozoa. 

 Are they abundant or few % What sort of 

 motions do they exhibit? Study their struct- 

 ure and endeavor to make out the liead — its 

 shape and relative size ; and the tail — its shape 

 and movements. Can you discover a cell-wall ? 

 Endeavor to stain the spermatozoa with hee- 

 matoxylin. What part becomes most deeply 

 stained ? Is this part a nucleus ? 



Draw a spermatozoon-. 



