60 COELENTERATA 



What conclusions can you make: first, as to the ability 

 to distinguish food; second, as to methods of obtaining food; 

 and third, in regard to ciliary action? 



3. Stimulate the animal with a needle at various points 

 and try to determine where it is most sensitive. Observe its 

 manner of contraction. When fully contracted, if the irrita- 

 tion is continued, threadlike structures, acontia, are thrust 

 out through minute pores, cinclides (sing, cinclis) , in the 

 body wall. 



Make a drawing of the contracted animal. 



Internal Anatomy. — Using preserved material, place the 

 edge of a razor across the peristomial area, at right angles to 

 the mouth-slit, and divide the animal from disk to base into 

 halves. 



1. Note the extent of the actinopharynx and siphono- 

 glyphs; they lead into the coelenteric chamber. Find the 

 extent of this chamber, and the method of its subdivision by 

 delicate partitions, the mesenteries, or septa. Are all of the 

 mesenteries alike? 



2. Forming the free edges of the mesenteries, below the 

 actinopharynx, are the convoluted mesenteric filaments, which 

 are secretory organs that are probably equivalent to the 

 gastric filaments of the Scyphozoa. 



3. Quite near the bases of the mesenteries are the attach- 

 ments of the acontia. What relation have they to the mesen- 

 teric filaments? Mount living acontia under a cover slip in 

 sea water and notice the central muscle strand, nematocysts, 

 and cilia. 



4. Also located on the mesenteries, and arranged parallel 

 to the filaments, but back from the edge a bit, are the repro- 

 ductive organs or gonads. Are they found on all of the mesen- 

 teries? The ova or spermatozoa are shed into the coelenteric 

 chamber and pass out through the mouth. 



Cut one of the halves of your specimen transversely in the 

 region of the actinopharynx, and study the arrangements of 

 the mesenteries, their attachments, etc. 



