PERSONAL AND CIVIC HYGIENE 343 



4. Find out just what happens when conjugation takes place. (Study 

 charts or Figures or text.) 



Conclusions. 1. Does there seem to be any reason why reproduction 

 does not go on indefinitely by simple division ? 



Note. "A freshening by the introduction of new vigor seems to be 

 necessary from time to time." ELECKEL. 



2. Then why should Protozoa conjugate, or "trade experiences"? 

 Note. In conjugation of paramoacia the traveling nuclei serve as male 

 traveling nuclei, while the nuclei remaining serve as female standing 

 nuclei. When the fresh nuclei have been formed, they separate. The 

 two new rejuvenated cells have once more acquired the power of renewed 

 activity and also of the ability to propagate by division for a time, or until 

 this power is exhausted, when conjugation must again take place. 



c. Metazoa 



1. FISH 



Observations. 1. Procure some fresh milt (sperm) of any fish most 

 conveniently at hand, as from the nearest state or government fish hatchery. 

 Also get some unfertilized eggs freshly ''stripped " from the body of the 

 female. Place some of the unfertilized eggs in a clean bowl, as a glass 

 finger bowl, and pour over them some of the milt or sperm. Set the 

 bowl aside in a moderate temperature. (This is known as artificial 

 fertilization.) Which are evidently the larger, sperm or eggs ? Which 

 are the most motile ? (Examine some with a compound microscope.) 



2. Place another lot of eggs in another bowl, and set aside with the 

 first lot, but unfertilized. 



3. Watch both lots for a few days. Which evidently increase in size ? 



4. Has fertilization evidently taken place in one lot ? Explain your 

 answer. Note. In nature the ova (spawn or eggs) of fishes are usually 

 deposited in the water in various hidden places on the bottom. The milt 

 or sperm is poured over them by the male, and the eggs are left to develop 

 with little or no care. 



5. Do you think that such habits would result in much care of the 

 young ? 



6. Note. The eggs of most sharks and such fishes are retained within 

 the body of the mother until they are hatched. 



7. Why should eggs be deposited in large numbers when they are laid 

 in the water ? 



8. Why are eggs fewer in number when they are fertilized within the 

 .body of the mother, and afterwards laid ? 



