40 ZOOLOGICAL EXERCISES. 
3. Place the animal and cork again in the saucer, and 
cover with salt-water.* Lift the integument of each 
ray in succession, and detach as far as possible the 
brown or bluish-green radial coca from the upper 
integument by breaking the folds of the mesentery 
which supports them. The yellow, or brownish re- 
productive organs will be seen hanging from the 
dorsal, or aboral surface at each inter-radial angle. 
Inside each of these organs is a vertical calcareous 
plate—the inter-radial septa—which connect the 
two surfaces. With a knife cut through these in 
succession, leaving the one next the madreporic 
tubercle until the last. Cut this very carefully so as 
~ not to injure the madreporic canal, or stone canal, 
which lies just inside of it. With the scissors cut 
through the dorsal integument up to the madreporic 
tubercle, from the side nearest to it, and then cut 
carefully close round it, so as to detach it from the 
resi. 
4. Gently raise the integument on the side opposite to the 
anus. Notice the short intestine running up to the 
anus, and the dark bluish, or brownish-green iter- 
radial coeca, or rectal cseca, opening into it. Cut the 
intestine with the scissors a little below these ceca. 
Remove the whole of the dorsal integument, and 
place it, exterior side downward, in another saucer of 
water. 
5. Take the dorsal portion. Examine the inter-radial 
ceca. With a fine brush spread them out and notice 
their number. Cut off a small portion and examine 
with the microscope. The function of this organ is. 
probably hepatic. 
* Fresh water will do, but it stops all ciliary movement. 
