MNEMIOPSIS. 33 



the terminal lobes, at a short distance from the mouth, notice a 

 small opaque spot, an undeveloped tentacle in its sheath. 



4. At the aboral pole is a depression, in the bottom of which 

 is the ''sensory body." 



5. Leading away from this and extending as meridional 

 lines toward the oral pole, are eight ctenophoral rows, or swim- 

 ming plates. Examine the plates with a hand-lens and deter- 

 mine their structure and function. A pair of rows (arising 

 from the pit of the sensory. body as a single row) extends down 

 over each terminal lobe. Another pair passes down each lateral 

 surface of the animal. Each of these lateral row^s, after passing 

 half-way to the mouth, changes its appearance somewhat, and 

 leaves the surface of the body proper, being continued down one 

 edge a'ud up the other of a finger-like process which hangs orally, 

 called an auricle. Each ctenophore then possesses four auricles, 

 w^hich are somewhat covered over by the loose edges of the 

 terminal lobes. The fringe of cilia which borders each auricle 

 is continuous with a fringe which extends up and down the 

 inner, lateral edge of each terminal lobe. Do you understand 

 how the animal gets its food ? 



Digestive System.— With a pipet inject a solution of carmine 

 into the mouth opening. 



1. You can then more plainly see the long ribbon-like esoph- 

 agus, which leads to a very small stomach just beneath the 

 sensory body. 



2. From the stomach are given off the canals, which in a 

 successful injection will be seen to be as follows: 



(a) Two short "excretory canals,'' opening into the pit where 

 the sensory body is located. 



(6) Two esophageal canals, one on each side, passing down 

 along the esophagus. 



(c) Two tentacular canals, one on each side, passing to the 

 tentacular structure of that side. 



(d) Four meridional canals, each of which bifurcates. The 

 eight thus formed pass dow^n the animal superficially, just beneath 

 the ctenophoral rows. 



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