GENERAL BIOLOGY 



swelling, globular in shape when seen from the face, flask-shaped 

 when seen from the side; they contain long, slender filaments 

 armed with barbs at the basal end. Run in a little iodine and ob- 

 serve the ejection of the threads of the nematocysts. Note that 

 the threads are turned inside out in the process of discharge, the 

 basal portion being discharged first. What is the use of the barbs? 

 The hollow thread ? The fluid in the cysts ? Do nematocysts occur 

 anywhere else than on the tentacles ? 



(d) The endoderm cells line the cavity of the tentacles. They 

 are large and some of them bear flagella by which currents are 

 caused. Focus on the middle of the thickness of a tentacle and 

 observe the flagella on the endoderm cells and the nutrient particles 

 streaming up and down the cavity of the tentacle. What difference 

 can you detect in the relative numbers of these elements (cells) in 

 the various parts of the body? 



Make drawings of a tentacle to show the characteristic layers, 

 and cellular elements. 



III. REPRODUCTION. 



1. Asexual reproduction occurs by the formation of hollow 

 out-growths from the sides of the body wall. Each of these acquires 

 a mouth and tentacles at the distal end of its body and finally, 

 constricting at the base, separates from the parent animal. Look 

 for such buds in various stages of development. 



2. Sexual reproduction: hydra is monoecious (hermaphro- 

 ditic), the same animal producing eggs and spermatozoa. 



(a) The spermaries are swellings of the body wall produced 

 by the local multiplication of interstitial cells, and covered on the 

 outside by a cap formed of large ectodermal cells. The spermaries 

 are situated just below the tentacles. How many do you find? Is 

 the number constant? Find a ripe spermary and observe the 

 movement of the spermatozoa within the capsule. By gentle 

 pressure upon the cover glass break open the capsule and observe 

 the swimming of the spermatozoa and their size and shape. 



(b) The ovaries usually develop later than the spermaries and 

 are formed near to the base of the animal. How many do you find? 

 Is the number the same in the brown and green species? Single 

 cells of each ovary enlarge to form the ovum, while the other cells 

 nourish it and form a capsule about it. 



Make drawings of buds and of the sexual or gams. 



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