PROBLEM 2. How More Complex Animals Reproduce 437 



9. Demonstration. Development of the chick. Stained microscopic slides 

 may be examined with a hand lens for the early stages. Look for the heart 

 and the beginnings of the nervous system in about thirty-six hours. Later 

 stages show the limb buds and the eyes. A museum preparation or a chart 

 will show the later development of a chick. Which part is proportionately 

 large in the early stages.^ At what stage does the embryo begin to look 

 like a bird? When do the feathers appear.' When are you sure that it is 

 going to be a chicken and not a duck? 



10. In review fill out a table. Rule vertical lines and write at the top 

 these headings: reproductive organs, secondary^ sex characters, gametes, 

 fertilization (whether external or internal), development (whether ex- 

 ternal or internal), care taken of young. Leave the last column without a 

 heading. Fill in the table for the following animals: codfish, frog, turtle, 

 snake, chicken, and deer. In the last column state if possible about each 

 animal whether the temperature necessary for development is obtained 

 through sitting on eggs, water warmed by sun, body temperature, hot 

 sand, or any other method. 



11. Answer these questions: {a) How does the family life of a social 

 insect like the ant differ from the family hfe of a bird? (Look back to 

 Unit I.) {b) "In general, the more complex an animal, the longer the pe- 

 riod of helplessness in babyhood." Cite examples that support this state- 

 ment. 



Further Activities in Biology 



1. If you have the use of an incubator study the development of the 

 chick. Be sure to get fertilized eggs, which can be bought from special 

 dealers. Start with twenty-four eggs. Turn them twice daily. Open one 

 every day. Perhaps someone could make models of the different stages. 



2. Guppies and some other tropical fish bear the young alive. You will 

 find it interesting to raise some. 



3. Pigeon raising is easy if you have the use of a roof. Get instructions 

 when you buy your first pigeons. 



4. If you have an opportunity to observe a litter of kittens, puppies, 

 white mice, or rats watch for indications of parental care. To what extent 

 are the young taught by their parents? 



5. Report on the work of Dr. Jacques Loeb on the artificial fertiliza- 

 tion of the eggs of the sea urchin. 



6. Raise tadpoles from frogs' eggs. 



7. Make wax or plaster models of the cleavage, hollow-ball (blastula), 

 and cup (gastrula) stages of some simple form such as the starfish. 



