68 STRUCTURE 



motile cilia. The cilia of some epithelia of vertebrates have short 

 non-striated rootlets. 



Striated ciliary roots have been reported from most of the 

 major groups of metazoa, viz. in vertebrates, pharyngeal cilia of 

 the frog (Fawcett and Porter, 1954) and retinal rod cilia of the 

 guinea pig and cat (Sjostrand, 1953; Tokuyasu and Yamada, 

 (1959); in molluscs, gill cilia oiMya and typhlosole ciHa of Elliptio 

 Fawcett and Porter, 1954); in ctenophores, the comb-plate cilia 

 of Pleurohrachia (Bradfield, 1955); in rotifers, coronal cilia of 

 Philodina (Lansing and Lamy, 1961a); in arthropods, cilia of the 

 scolopale organ of Locusta (Gray, 1960); in annelids, cilia of 

 Luvibricus and in ectoproct polyzoa, cilia of Pectinatella (Fawcett, 

 1958b). Generally these roots have a single origin and may branch 

 later into many rootlets which ramify through the cell, but in 

 the molluscs mentioned two roots arise from each basal body, and 

 three roots leave each basal body in Pectinatella. The roots 

 extend to about the level of the nucleus in most epithelial cells, 

 while the sensory cilia in the vertebrate retinal rod and the locust 

 scolopale organ have very long roots, extending to 80 or 100 /x in 

 the latter case. 



The appearance of the striated root of the locust scolopale 

 cilium is shown in Plates VI d and XI Vb, where each repeating 

 unit of the root can be seen to be made up of six bands. Strikingly 

 similar bandings are seen in the roots of rotifer, annelid, (PI. XI Va), 

 mollusc (PL XI Vc) and polyzoan cilia, as well as in the kineto- 

 desmata of Paramecium (Sedar and Porter, 1955) and the costa of 

 Tritrichomonas (see p. 71). 



In Anodonta, Gibbons (1961b) has been able to correlate the 

 position of attachment of structures to the basal bodies of the 

 cilia with the direction of ciliary beat. Near the inner end of the 

 basal body is a conical structure (the basal foot) which projects 

 laterally from peripheral fibrils 5 and 6 (Fig. 7G and PI. Ila, b), 

 and is therefore on that side of the cilium towards which the 

 effective stroke takes place. It is about 0*15 i^t long and 0*1 /la 

 wide and shows slight evidence of a transverse striation. In 

 frontal cilia at least, three striated roots, one large and two small, 

 run down into the cytoplasm from the inner end of the basal body. 

 All three have a striation period of about 750 A, within which up 

 to twelve intraperiod striations may be seen in some cases, and 



