46 COELENTERATA 



5. The fleshy continuation of the zooid down into the 

 stalk is termed the coenosarc. Is it in close contact with the 

 perisarc? 



6. In an expanded hydranth, note the mouth, the arrange- 

 ment of the tentacles, and the number of tentacles. How is 

 the individual supported in the hydrotheca? Trace the 

 coelenteric cavity through branches and hydranths and de- 

 termine whether it is continuous. 



7. Can you determine what keeps the fluid in the cavity 

 in motion? 



8. Examine a hydranth with a high power and look for 

 the cell layers characteristic of coelenterates. Determine how 

 its tentacles differ from the tentacles of Hydra, and explode 

 nematocysts as in Hydra. 



Make a drawing of a hydranth. 



9. Look for certain extremities which show neither ten- 

 tacles nor any opening in the outer covering. Such a con- 

 dition signifies either an immature hydranth or a reproductive 

 individual. If the latter, it is considerably swollen and is 

 termed a gonosome. The central core of a gonosome, the 

 blastostyle, should be examined for gonophores, frequently 

 called medusa buds. This may require a high power. De- 

 termine how the gonophores are arranged around the blas- 

 tostyle. Are all in equal stages of development? What 

 relation has the end of the blastostyle to the outer covering, 

 the gonangiumf 



Make a drawing of a gonosome. 



10. The free medusae are small, transparent, and easily 

 overlooked. During the breeding season they may usually be 

 found in abundance in dishes in which colonies have been 

 kept over night. Notice their movements and their positions 

 while at rest on the bottom. The number of tentacles and 

 the position of the sense organs is definite for the species. 

 Two species that differ in the number of tentacles are com- 

 mon at Woods Hole. The inverted bell with the manubrium 

 sticking out from the convex surface of the resting specimen 



