14 THE FROG 



examine it with the high power. The cells are imbedded in 

 a matrix, produced by the cells. If the material is fresh 

 the cells will be alive, but the intercellular substance is al- 

 ways lifeless. Sketch a small portion of the cartilage, show- 

 ing cells and matrix. 



4. Reproductive Cells. Using the low power of the 

 microscope, examine a cross-section of the immature ovary 

 of a frog, and sketch a portion of the ovarian wall showing 

 the young ova or egg cells. Observe the large size of the 

 nucleus, here called the germinal vesicle. 



Examine a stained preparation of the reproductive cells 

 (spermatozoa) of the male frog or salamander. These are 

 elongated thread-like cells. Under high power, distinguish 

 two main portions of a spermatozoon, head and flagellum. 

 The head consists mainly of the deeply-stained nucleus, but 

 tapers to an extremely fine transparent point, the acrosome. 

 The flagellum is extremely slender and almost colorless. 

 Sketch a spermatozoon, representing it about ten centimeters 

 in length. 



5. Cell Division. Read an account of indirect cell divi- 

 sion or mitosis. With the high power of the microscope 

 study dividing cells in prepared material which will be fur- 

 nished. If the material is limited in amount, a demonstra- 

 tion series will be prepared by the instructor. Sketch as 

 many different stages as you can find, and number these in 

 the correct order. 



