FIBRILLAR SYSTEMS IN THE MITOTIC APPARATUS 177 



in vitro and in vivo systems may be only coincidence, with no fundamental 

 mechanism in common. I don't feel justified in speculating further on what 

 is responsible for bringing the precursor molecules sufficiently close to one 

 another for short-range forces to bind them together into the definitive mitotic 

 apparatus. 



Dr. Giese (Stanford University): Has any study been made of the con- 

 stituents of the centriole and their effect on spindle formation? 



Dr. Went: No, not that I am aware of. However, this problem is now 

 under investigation in Professor Mazia's laboratory. It is in its infancy, for a 

 method still has to be perfected whereby centrioles, or their constituents, can 

 be freed from undesired cytoplasmic matter. Then it is a question of whether 

 or not enough material can be obtained, for the centriole is a very small entity. 



