Branch Coelenterata 25 



b. The connection of the base of the hydranth to the 

 protoplasm in the stem of the perisarc. 



c. The shape of the body, including its basal part, its 

 central part, the tentacles, the proboscis or manu- 

 brium upon the tip of which is the mouth. 



VI. — Compare this hydranth with a Hydra. In what re- 

 spects does it resemble the Hydra ? In what respects 

 does it differ from it .? 



VII. — Study the tentacles carefully, using as high power 

 as necessary. How many are there .' Is the number 

 always the same on different hydranths ? How does 

 their length compare with the length of the body of 

 the hydranth .'' See the little nettle cells. How are 

 these arranged .■" 



VIII. — • Study the different stages of the young hydranths. 

 Make drawings of two or three of these stages. Are 

 these young hydranths able to get food for themselves.'' 

 If not, where does the material for their growth come 

 from } 



IX. — Trace the connection between a hydranth and the 

 one next above it and next below it on the stem. Is 

 the protoplasm continuous 1 Can you find any in 

 which a fully developed hydranth with tentacles is next 

 to a partially developed hydranth .'' 



X. — Make a careful drawing of a gonangium, showing the 



club-shaped perisarc portion and the round or oval 

 bodies inside, as well as the protoplasmic connection 

 with the main stem. The bodies inside are medusa- 

 buds. In due time they escape from the club-shaped 

 perisarc into the sea, where they develop into small, 

 free-swimming jelly-fishes, very different from the hy- 

 droid colony. There are thus two sorts of generations 

 of this animal — the fixed colony you have been study- 



