CCELBNTEKATA. 23 



4. Observe the digestive cavity outlined through the 



semi-transparent body wall of the hydranth. 



5. Is there a transparent sheath around the hy- 



dranth ? 



6. Where are the medusa-buds attached ? 



7. Are the medusa-buds of uniform size ? 



8. Observe the digestive cavity within a large medusa- 



bud. 



These medusa-buds drop off into the water and then enlarge 

 into medusa (see Number 4 in Study III. on p. 23). These 

 medusae produce eggs from which develop new liydroid colonies 

 like their grandparent form. This manner of reproduction is 

 called alternation of generations. 



D. Drawings. 



1. An entire colony. 



2. A fragment of a colony enlarged to illustrate A 2. 



3. A hydranth with medusa-buds, enlarged still more. 



4. A HYDRO-MEDUSA. 



(This is the alternate generation of a hydroid.) 



A. Observe its general hemispherical shape. The con- 



vex side is termed the ex-umbrella side, and the 

 animal swims with this side up. The flat side is 

 termed the sub-umbrella side. 



B. Carefully place the specimen with the sub-umbrella 



side up and make out the following points : — 

 1. Tentacles. 



a. A little pad near the distal end of each tentacle. 

 (By means of these pads, which act as suckers, the 

 animal attaches itself to the floating seaweeds. )i 

 1 See footnote on p. 24. 



