The Two Components of Semen 1 



piece, but by the time the spermatozoa have reached the cauda 

 epididymidis and are nearing the vas deferens, the droplets take up 

 a position at the distal (posterior) end of the middle-piece (Merton, 

 1939; Fig. 2). Finally, they tend to disappear altogether and are 

 seldom found in ejaculated sperm, except m certain abnormal cases 

 (Plate I). Some authors regard the kinoplasmic droplet as no more 

 than a remnant of spermatid cytoplasm devoid of special signi- 

 ficance, but there are those who believe that it plays an important 

 role by nourishing the spermatozoon during the passage through the 

 epididymis, before the sperm cells establish contact with an extra- 

 cellular source of nutrient material, in the form of seminal plasma. 

 The disappearance of the kinoplasmic droplet is but the final 

 stage in the process of gradual shrinkage and 'dehydration' of proto- 

 plasm which accompanies both spermatogenesis and ripening, and 

 from which the 'ripe' spermatozoon ultimately emerges as a cell 

 with a highly condensed nucleus and very little cytoplasm. Associated 

 with the diminution of protoplasm is a progressive loss of water 

 and a corresponding increase in the specific gravity of the sperm cell. 

 Lindahl and Kihlstrom (1952) suspended equal numbers of bull 

 spermatozoa in a series of aqueous solutions of 

 the methylglucamine salt of 'umbradil' (2 : 5-di- 

 iodine-4-pyridone-A^-acetic acid), the lightest of 

 which (sp. g. 10918, osmotic pressure 18 atm.) 

 had a lower specific gravity than any of the 

 spermatozoa, the heaviest (sp. g. 1-3519, osmotic 

 pressure 220 atm.) being of about the same 

 specific gravity as the 'densest' spermatozoa; 

 these sperm suspensions were centrifuged in 

 haematocrit tubes so that all spermatozoa with 

 a specific gravity exceeding that of the medium, 

 formed a sediment in the graded capillary part of 

 haematocrit tubes. The specific gravity of bull 



Fig. 2. ''Ripening'' process in the epididymis of the 

 mouse; (a) spermatozoon from the caput epi- 

 didymis with proximal kinoplasmic droplet; 

 (b) spermatozoon from the cauda epididymis 

 with distal kinoplasmic droplet. 



(Merton, 1939) 



(i 



