some 400 references are mentioned here, recent work being 

 cited more fully (well over half the references date within the 

 last 10 years), while key works are quoted from older studies to 

 enable interested students to follow up other references. 



While the review was written to satisfy the needs of the honours 

 student of Zoology, students in other fields should also find it 

 valuable. Research workers studying any topic related to ciliary 

 organelles or their activity should find it useful as a fairly concise 

 summary of the structure and physiology of cilia, particularly 

 since most reviews tend to concentrate on either structure or 

 physiology with little reference to the other part of the subject. 

 Where good evidence is available I have tried to keep closely to 

 established facts, but where our knowledge is very scanty I have 

 tended to stray into the realms of speculation; I hope that the 

 reader will be able to distinguish facts from speculative suggestions. 



Few can fail to be convinced of the need for such a review at 

 this time, and I hope that this attempt at a summary of the 

 present position will satisfy the requirements of as many people 

 as possible. If any of the ideas presented here will lead others 

 to further research, then the author will be well satisfied that he 

 has not laboured in vain. 



Vll 



