74 STRUCTURE 



6. Haptonemata 



Several species of biflagellate algae of the genus Chryso- 

 chromulina (Chtysophyceae) (Parke, Manton and Clarke, 1955, 

 1956, 1958, 1959; Manton and Leedale, 1961) and the motile 

 phase of a coccolithophorid known as Crystallolithus hyalinus 

 (Parke and Adams, 1960), carry an appendage of much the same 

 dimensions as a flagellum (PL IXd) which lacks the characteristic 

 form of flagellar motility and may coil to the shape of a spring. 

 Parke, Manton and Clarke (1955) have proposed the name 

 haptonema for this structure, since it is thread-like and has an 

 adhesive area. 



In the small species the haptonema may be only about 5 fi long, 

 but in Chrysochrotnulina strohilus lengths of up to 200 /a were 

 reported; the diameter in all cases seems to be between 0'15 and 

 0'2 jJL. Internally there are three concentric membranes, the 

 outer one at least being similar in thickness to a ciliary membrane 

 (PI. IXe). These membranes surround a ring of longitudinal 

 fibrils, 6 in some species, 7 or 8 in others. Each fibril appears 

 tubular in transverse section, and has a diameter of 200 to 250 A. 

 No good evidence is yet available about the basal structure, which 

 may give valuable information about the homology of these 

 structures. All the haptonemata found have been extensible (and 

 also contractile?) structures, which act as means of attachment, 

 having either a clubbed adhesive tip, or an adhesive area along 

 the whole length as in C. strohilus. 



7. " Stereocilia '' 



Non-motile structures similar in appearance to normal cilia, 

 but with reduced internal structure, have been described from 

 mammalian epithelia by Wersall (1956), Yasuzumi and Wakisaka 

 (1956) and Nilsson (1957). These structures were first described 

 from epididymal cells by Aigner (1900), but the name stereocilia 

 was suggested by Reichel (1921). Aigner recognized that they 

 were not true cilia, and Lucas (1932c) has summarized further 

 evidence that they have different nature. The use of the electron 

 microscope has demonstrated this conclusively, and Yasuzumi 

 and Wakisaka found that stereocilia from rat epididymis were like 

 long swollen microvilli, lacking internal fibrils. 



Stereocilia found by Wersall in the cristae ampullares of the 



