76 GENERAL BIOLOGY 



buds, and -this budding is the common method of repro- 

 duction. What become of the buds? Are colonies formed 

 by budding? Why? 



Make an outline drawing of the animal in the expanded 

 condition, and one of the contracted animal. 



2. Minute Structure. Place the dish containing the hydra 

 on the stage of the compound microscope and examine with 

 the low power; or place the hydra on a slide and cover with 

 a cover glass, supporting the latter to prevent crushing the 

 animal. Is there a cavity (the enteron or digestive cavity) 

 in the animal? Does the cavity extend into the tentacles? 

 Sometimes small particles may be seen floating in the cavity 

 of the body or tentacles, or even passing from the enteron 

 into the tentacles. From this fact what inference may be 

 drawn as to the structure of the tentacles and their mode 

 of nutrition? 



Observe that the body is composed of layers (tissues), 

 an outer ectoderm and an inner entoderm. Which of these 

 layers is thicker? Are the layers made up of cells? In 

 which layer is the coloring matter located? Is the color 

 evenly diffused or is it segregated into distinct bodies? 



Draw a portion of the body enlarged to show the layers; 

 also show the cells if it is possible to determine their outlines. 



With the high power observe an extended tentacle. Do 

 you find ectoderm and entoderm? Are cells present? Note 

 the knobs on the tentacles, composed of oval, transparent, 

 bladder-like bodies or cells. These are the stinging cells 

 (nematocysts or thread cells) which represent modified 

 ectoderm cells. Where are the nematocysts most abundant? 

 Is there any definite arrangement of these cells? From 

 the outer end of each of these cells projects a stiff hair-like 

 process, the trigger or cnidocil. Within the capsule of the 

 cell is a coiled thread which may sometimes be made out 



