GAMETES 



275 



flagellum can be split. Eight of these microfibrils are arranged in a 

 tube and their ends are connected to the base of 

 the head. They surround the ninth microfibril. This 

 central fibril is fastened to the centrosome which is 

 situated in the crater-shaped base of the head. 

 These 9 microfibrils are enveloped by a helical 

 sheath consisting of a double spiral, each band of 

 which is about 1 70 m// thick. The spiral body origin- 

 ates from mitochondria; it is rich in lipids. It 

 ends with the so-called ring of Jensen who had 

 discovered the spiral body in the ordinary micros- 

 cope (1887). Further on the axon is covered by a 

 thin cortical membrane, which again has a helical 

 texture (tail spirals). It consists of microfibrils about 

 50 m// thick with a low pitch making about 150 

 spiral windings around the axon. 



The terminal part of the tail protrudes from the 

 cortical membrane showing the uncovered axon. 

 Usually this part is slightly curved or sharply bent 

 at the end (Fig. 137). When bull sperm is dried, 

 the microfibrils of the axon fall apart, forming a 

 tiny brush which is an artefact. In human sperm 

 this is not the case. 



It is remarkable that the number of 9 microfibrils 

 is not only characteristic for the sperm tail of many 

 vertebrates (e.g. Corregonus; Rotheli, Roth and 

 Medem, 1950), but also for some invertebrates 

 investigated, such as sea-urchins and coleoptera 

 (Bretschneider 1948). In ram spermatozoa 12 

 microfibrils have been found (Randall and Fried- 

 lander, 1950), 6 of which form a tube surrounding 

 a sixfold central fibril. Minute details of the connec- 

 tions of the tail fibrils to the head and the compli- 

 cated helical textures of the spiral body and the corti- 

 cal membrane are also described by these authors. 



In algae there are spermatozoa with hairy flagella 

 (in German "Flimmergeisseln"). With Euglena and Monas the hairs 

 have been discovered in the ordinary microscope (Fischer, 1894). 



Fig. 137. Fine- 

 structure of the 

 sperm (from Bret- 

 schneider, 1949). 

 I head cap ; 2 chro- 

 mosomes ; 3 head 

 tunica (external 

 layer) ; 4 ring- 

 shaped membrane ; 

 5 centrosome; 6 

 articular strands ; 



7 axial filament; 



8 double helix 

 (Jensen's spiral 

 body); 9 Jensen's 

 ring; 10 cortical 

 helix; 11 terminal 



piece. 



