17 



aration affords a demonstration that young ova are single cells with 

 nucleus and cell-body. Sketch one or more that show typically. 



2. Ovarian Ova. Amblystoma. Demonstration. Study, 

 recognizing in the young ova nucleus and cell-body. Compare 

 with (i). 



3. Early blastula stage. Amblystoma. Assigned for study. 

 At this stage the fertilized ovum has divided up into a few cells, 

 arranged in a single layer around a central cavity (blastoccele), 

 comparable to a simple epithelium. Make a sketch showing out- 

 lines of cells and, if possible, of nuclei. 



4. Late blastula stage. Amblystoma. Assigned for study. 

 The cells at this stage have greatly increased in number, are smaller, 

 and the wall bounding the cavity is of several layers of cells, com- 

 parable, therefore, with a stratified epithelium. Sketch, showing 

 the outline of the egg, the outline of the cavity, and for a portion of 

 the wall, the outlines of the cells and nuclei. 



5. Medullary plate stage. Amblystoma. Assigned for 

 study. At this stage differentiation is well advanced. The three 

 germ layers are seen in the section ; from the entoderm the noto- 

 chord is forming ; from the ectoderm, the central nervous system ; 

 the cavity is the alimentary canal (archenteron). Sketch the dorsal 

 portion, and compare with the figure in the text-book. 



TOPICS FOR QUIZ 4th Week. 



INTRODUCTORY AND TECHNIC ; THE CEI,L AND THE TISSUES. 



1. Histology, define; what is a cell, nucleus, cell-body; a tissue and its 

 composition, kinds of tissue ; intercellular substance? 



2. What is an ovum, and how are the tissues derived from it? 



3. What are the ways of examining animal tissues with the microscope ? 

 What is isolation or dissociation ? Give examples. What is fixing and why 

 necessary? What is meant by imbedding, its aim, when necessary? Name 

 three methods. 



4. Staining, what is it, why advantageous ; kinds of staining and of stains 

 used in histology. 



5. Mounting, kinds of mounting media ? Give exact procedure in mount- 

 ing in (a) glycerine ; (b) in glycerine jelly ; (c) in balsam. 



