Fig. 25. A model of an icosahedron doubly 

 shadowed. Note two shadow shapes which 

 can be cast simultaneously only by an icosa- 

 hedron in this orientation. 



Fig. 26. Frozen-dried particles of the tipula 

 iridescent virus doubly shadowed. Note simi- 

 larity to shadows in Fig. 25. (Magnification 

 X 53,000.) 



Fig. 27. Section through the nucleus of a 

 blood cell from T. paludosa infected with its 

 polyhidrosis. Note the apparent development 

 of the virus rods in the central chromatic mass. 

 (Magnification: X 28,000 



Fig. 28. Later stages of the same disease as 

 in Fig. 27. Note the fully formed virus rods, 

 some with enclosing membranes. (Magnifica- 

 tion: X 25,000.) 



