FINE STRUCTURE 57 



where the two central fibers end, and there also is to be seen a 

 " kinetosome " or ampule terminating the central fibers. According 

 to the latter report, the base of the cilium, with its prolongation 

 of the peripheral fibers, continues inward as a cylinder without 

 rootlets extending into the endoplasm but sometimes showing 

 minute granules in longitudinal rows along its cylindrical wall.* 



6. Fine structure of the nuclei 



Light microscopists describe the matrix of the macronucleus as 

 of homogeneous granules in a sort of meshwork with one clear 

 spherule, the nucleolus, usually found in each node of a chain 

 nucleus. The nuclear membrane swxUs loose in distilled water 

 as a highly birefringent and therefore well-organized layer; 

 significantly Hke the shell of the pigment granules, its composition 

 was indicated to be phospholipid (Weisz, 1949a). Resting on the 

 macronuclear membrane. Park (1929) described osmiophihc, 

 bleb-Hke bodies, i to 22 for each node. He suggested that they 

 might be secretory droplets, reminiscent of the parabasal body 

 associated with the nucleus in flagellates. 



Electronmicrographs reveal further details (Faure-Fremiet and 

 Rouiller, 1955; Randall and Jackson, 1958). The granules within 

 the macronucleus turn out to be clusters of filaments, possibly 

 beaded, these masses being more or less equidistantly spaced 

 within a clear nuclear sap. The outer layer of the macronucleus 

 is porous, showing curious tubular processes extending and 

 branching into the endoplasm, w^hile the inner membrane appears 

 to be a system of tubular vesicles joined by sheets, resembling 

 spaghetti laminated in plastic. 



In his cytochemical studies, Weisz (1949a, 1950b) made 

 Feulgen and Millon tests which indicate that protein and nucleo- 

 tide or potential nucleotides are homogeneous in concentration in 

 the macronucleus at all times, except of course during conjugation 

 when the old macronucleus is resorbed. His methyl green tests 

 suggested however that the nucleotide. — desoxyribonucleic acid — 



*From observations on stentor membranelles, Sleigh (i960) ingeniously 

 integrated motor and recovery strokes of cilia as resulting from one wave 

 of localized contractions passing up and around the cilium, the propulsive 

 phase occurring when bending starts on one side at the base and the rest 

 of the cilium is straight. 



