70 



ANIMAL BIOLOGY 



Pick off the pieces of shell and allow all the contents of the shell 



to flow out into a cup, or deep saucer, taking care not to 



break the yolk. 

 a. State what has been done, and describe the position and color 



of the white and of the yolk of the egg. 

 6. Note two twisted strands extending from the yolk towards 



each end of the egg. These help to protect the yolk from 



sudden jars. Describe the position, appearance, and use 



of these strands. 

 Carefully turn the yolk until you notice a white spot. This spot 



is the beginning of an embryo chick. 

 Describe the position and appearance of a young chick embryo. 



54. Reproduction and life history. — In the preceding 

 section we have seen that a bird's egg consists of a hard 



shell, a membrane, the white 

 and the yolk ; and that on the 

 outer surface of the latter is a 

 tiny embryo. Let us now see 

 how this egg is formed and 

 developed. 



In our study of seed-plants 

 we learned that plant em- 

 bryos are formed in the ovary 

 of a pistil after an egg-cell 

 has been fertilized by a sperm- 

 cell. In the case of insects (22, 27) and the fish (104) 

 we find that egg-cells are produced in organs of the female 

 known as ovaries arid that before an egg-cell can develop 

 into an embryo (except in rare cases) it must be fertilized 

 by a sperm-cell (Fig. 53) which has been formed in the 

 spermary of a male. 



If the ovaries of a hen are examined, they will be found 

 to consist of a large number of spherical objects, the larger 



Fig. 53. 



- Sperm-cells of various 

 animals. 



