28 CCELENTERATA. 



live specimens, however, prove that the animal is sensitive over 

 this area as elsewhere. 



Preserved and hardened material is better than living for the 

 study of the rest of the anatomy of this form. With a specimen 

 in water in a finger-bowl, with a black tile for the background, 

 find the following from the sub-umbrellar surface: 



1. The shape of the animal. Is the margin perfectly circular 

 or regularly indented? Are all of the marginal portions similar? 



2. Four large, fringed oral arms or lips hang from the corners 

 of the nearly square mouth, which is located in the center. No- 

 tice 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 may not be entangled. 



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

 spacious stomach, which is produced in the region between each 

 two corners of the mouth to form a gastric pouch. 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 circumferential canal 



(a) Directly beneath each oral arm a per-radial canal is given 

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

 branch on either side. The per-radial canal proper usually 

 continues straight to the marginal circumferential canal, without 

 further subdivision, but the two side branches above mentioned 

 in turn subdivide several times. 



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

 canals pass toward the margin; the middle one (inter-radial 

 canal) branches somewhat after the manner of the per-radial 

 canals, but the other two (ad-radial canals) continue to the 

 circular canal without further branching. 1 



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

 not, they may be injected with wafer in which carmine is mixed, by insert- 

 ing a large-mouthed pipet into the stomach. 



