SPERM ATOGENESIS INSEMINATION 



169 



and Thomson, 1 who believe it to exemplify those katabolic pheno- 

 mena which, according to their view, are usually associated with the 

 male sex. 



a 



d 



9 



FIG. 54. Different forms of spermatozoa from different species of 

 animals, as follows : 



a, Bat ; b and f, frog ; c/, finch ; e, ram ; /'and #, boar ; k, jelly- fish ; 

 ;', monkey ; , round worm ; I, crab. (From Verworn.) 



SEMINAL FLUID 



The semen serves as the mechanical medium in which the 

 spermatozoa move. It is possible also that it has a nutritive function. 

 It is secreted by the seminiferous tubules. It is milky in appearance, 

 and has a characteristic smell. When ejected the seminal fluid is 

 mixed with the secretions of the accessory glands (prostate, etc.), 

 which render it still more milky. On standing it tends to become 

 gelatinous. According to Lode, 2 the specific gravity of semen is 

 between 1-027 and T046. 



The number of spermatozoa which exist in normal human semen 

 is subject to much variation. Lode 3 has shown that it diminishes 

 almost to zero after a number of successive emissions, but increases 

 again after an interval of several days. The average number is 

 given as 60,000 per cubic centimetre. The number of sperms 

 present in the ejected seminal fluid of the dog was also found to 

 be greater at the end of an interval in which there were no emissions, 

 but it did not continue to increase after more than eight or ten days. 

 In a normal emission of semen (man) Lode calculates that there are 



1 Geddes and Thomson, The Ecolntioit of $<.:>', Revised Edition, London, 1901. 



2 Lode, " Untersuchungen iiber die Zahlen- und Regenerationsverhaltnisse 

 der Spermatozoiden bei Hund und Mensch," Pfliiger's Arc/i., vol. 1., 1891. 



3 Lode calculates that about 339,386,500,000 spermatozoa must be produced 

 in man between the ages of twenty-five and fifty- five. 



6 A 



