40 STRUCTURE 



the cilia of ctenophore comb -plates (p. 32). Granules about 180 A 

 in diameter are found on the inside of the cell membrane of the 

 wall of the groove, exactly opposite some of the peripheral fibrils 

 of the flagella (PL I). Fine filaments run across the extracellular 

 gap from these granules to a small dense mass inside the flagellar 

 membrane, and probably penetrate both membranes. From here 

 they can be traced to a termination at a ridge of dense material 

 at the junction between the two subfibrils on the outer side of a 

 peripheral fibril. Gibbons and Grimstone interpret these linkages 

 as filaments rather than lamellae because distinctly separate 

 granules can be seen on the groove wall in longitudinal sections. 

 The rare interflagellar connexions of Pseudotrichonympha link 

 peripheral fibril 3 of one flagellum to peripheral fibril 8 of the next 

 flagellum (cf. ctenophore comb -plate) by means of a filament that 

 crosses an interflagellar gap of 100 A or more. 



Manton (1959a) has described the unusual shape of the flagellum 

 of the minute flagellate Chromulina pusilla^ which deserves a 

 mention, although it appears to be based on a normal constructional 

 plan. The whole flagellum is only about 3 to 4 ^ long and is 

 sharply divided into two parts, with a 1 /x long basal portion about 

 1500 A in diameter containing the normal 9-plus-2 fibril pattern 

 connected to a normal basal body, w^hile the distal 2 or 3 ^t form 

 a long whiplash about 500 A in diameter which apparently 

 contains only the two central fibrils (PL VIIIc). 



Outside the flagellar membrane of the anterior flagellum of 

 Peranema are two longitudinal half -cylindrical sheaths of striated 

 material. These have been described by Chen (1950), Pitelka and 

 Schooley (1955) and Roth (1959). The electron micrographs 

 published by Roth show that in transverse sections the sheath 

 appears to be built up from 4 to 6 layers about 100 A apart and 

 100 A thick, composed of material that in longitudinal section 

 has a transverse striation with a periodic spacing of about 450 A 

 (PL Vllb). This structure deserves further study at high magni- 

 fication to discover its means of attachment to the flagellum and 

 perhaps finer details of structure. 



Sperm Tails 



Some animal sperm lack flagellar tails, e.g. the sperm of the 

 crustacean ProcambaruSy in which, nevertheless, normal centrioles 



