178 A GUIDE FOR THE STUDY OF ANIMALS 



from time to time and note difference in appearance, as 

 development proceeds, especially as to transparency and 

 size of the air space. An egg that is transparent after ten 

 days is probably infertile and should be removed. Eggs 

 which are developing properly will show from this time on 

 a well- developed air space, and will be quite opaque. The 

 veins often give a spider-web appearance. 



Twice each day remove the tray of eggs and allow to 

 cool slightly. Once a day the eggs should be turned be- 

 fore the tray is returned to the incubator. 



Questions. 



1. Describe the appearance of the shell when the chick 

 is about to come out. In about how many days after you 

 put the eggs in the incubator did you first note this change 1 

 You should watch the incubator carefully from the eigh- 

 teenth day on. , 



2. What proportion of the eggs hatched ? What reasons 

 can you suggest for the failure of some to hatch .' Did any 

 which were pipped fail to hatch .-' If so, break them open 

 and see if you can discover the trouble. 



3. How does the chick get out of the shell? How long 

 does it take for it to get out after the shell is chipped ? 

 How does a chick look as soon as it has come out of the 

 shell .? 



4. With what is a chick covered when it is first hatched.-' 

 How long before feathers begin to develop .<' 



5. How long before a chick needs food .' How does it 

 recognize it .■" 



Summary. 



1. What are the two kinds of development .-' 



2. What are the stages in embryonic development .-• 



