56 COELENTERATA 



corners of the nearly square mouth, which is located in the 

 center. Notice how each arm is similar to a long, narrow 

 leaf, with the sides folded, especially along their margins. 

 Examine the arms for nematocysts. Do you understand how 

 the animal gets its food? If the arm edges appear to be 

 covered with dark specks and granules, examine to see if 

 embryos are entangled there. 



3. The mouth is found to lead by a short gullet into a 

 rather spacious stomach, which is produced in the region be- 

 tween adjacent corners of the mouth to form a gastric pouch. 

 In each of the pouches are a number of gastric filaments. 

 Determine the shape of the stomach. 



4. The remaining parts of the digestive (and also in this 

 case circulatory) system include the numerous radial canals 

 and the single circular canal. 



(a) Directly beneath each oral arm a perradial canal is 

 given off, which, at a short distance from the stomach, gives 

 off a branch on either side. One portion of the perradial 

 canal continues straight to the margin and joins the circular 

 canal, without further subdivision, but the two side branches 

 in turn subdivide several times. 



(b) From the peripheral wall of each gastric pouch three 

 canals pass toward the margin; the middle one {interradial 

 canal) branches somewhat after the manner of the perradial 

 canals, but the other two (adradial canals) continue to the 

 circular canal without further branching. 1 



5. The position of the gastric pouches is made clearly 

 manifest by the gonads, which lie on the floor of the pouches, 

 as frill-like structures, horseshoe-shaped, with their open 

 sides toward the mouth. The ova or spermatozoa are shed 

 into the stomach and pass out of the mouth. Embryos in 

 various stages of development may frequently be found ad- 

 hering to the oral arms. The sexes are separate. On the sub- 



1 In most cases the foregoing canals are very evident, but if they 

 are not, they may be injected with water in which powdered carmine 

 is mixed, by inserting a large-mouthed pipette into the stomach. 



