STRUCTURE OF THE STARFISH. 73 



XI. THE MICROSCOPIC STRUCTURE OF THE 

 STARFISH. 



THE smallest specimens which can be procured should 

 be placed in a quantity of one-half per cent solution 

 of chromic acid for about twelve hours. They should 

 then be transferred to a quantity of one per cent chromic 

 acid, in which they should remain until most of the cal- 

 careous matter of the skeleton has been dissolved. 



With specimens an inch long or less this should be 

 accomplished in twenty-four hours, but larger specimens 

 may require several days, and in this case the chromic acid 

 should be renewed every da}'. 



When decalcified the specimens should be placed in 

 eighty per cent alcohol for twenty-four hours, and they 

 may then be preserved in ninety per cent or ninety-five 

 per cent alcohol until they are to be examined. 



I. Cut oft* one of the arms, stain and mount it as 

 directed in Section VII., and cut a number of transverse 

 sections. 



Examining it with a magnifying power of from twenty- 

 five to fifty diameters, notice : 



a. The remains of the calcareous ossicles (Fig. 32, 6, j?, 

 and 7) imbedded in the integument. They will probably 

 retain enough of their calcareous matter to show that they 

 are formed of a network of calcareous rods or spicules 

 arranged in rows pretty nearly concentric with the outer 

 surface. 



b. Notice that the spines (Fig. 32, g) of the ab-oral 

 surface are continuous with the ab-oral ossicles. 



1. Around the bases of these spines notice the pedicel- 

 Iaria3 (f), made up of a shaft and two blades. Notice - 



