CHAPTER 1 



INTRODUCTION 



Cilia seem to have been seen for the first time by the Dutch 

 microscopist Leeuwenhoek in 1675. In a letter to the Royal 

 Society (Leeuwenhoek, 1677), he described the incredibly thin 

 feet or little legs by means of which a small animalcule, which 

 Dobell (1932) believes to have been a ciliated protozoon, moved 

 through the water. Cilia, or the immediate result of their move- 

 ments, were seen in metazoa at about the same time by de Heide 

 (1684), who described a " motus tremulus " of the gill surface of 

 Mytilus. These authors did not give these little legs any special 

 name, and O. F. Miiller (1786) seems to have been the first to use 

 the name cilia, probably from the similar appearance of a group of 

 cilia to eyelashes. The name flagellum seems to have a more 

 recent origin, and is perhaps due to Dujardin (1841), who used the 

 term flagelliform to describe the appearance of cilia on some 

 protozoa. 



By 1835 cilia had been found in most of the main animal groups, 

 and the first comprehensive reviews about these organelles were 

 written by Purkinje and Valentin (1835) and Sharpey (1835). To 

 the former authors goes the credit for the discovery of cilia in 

 mammals in 1834. Sharpey described cilia observed by himself 

 and others in protozoa, sponges, coelenterates, ctenophores, 

 turbellarians, rotifers, annelids, molluscs, echinoderms, ectoprocts, 

 tunicates and vertebrates. In addition to reviewing the functions 

 of the cilia in these various groups, Sharpey made some interesting 

 comments on the structure and physiology of cilia. Some authors 

 of that time, including Ehrenberg^ (1832) and Purkinje and 

 Valentin (1835), seemed to be of the opinion that ciHa were moved 

 by small muscles attached to the bulbous base of the cilia, while 

 Grant (1835) suggested that they might move by the flowing of 

 water into and out of a tubular organelle. Sharpey, however, put 



