REPRODUCTIVE ORGANS IN ANIMALS 39 



parts become turgid. In the female the complete orgasm satisfy- 

 ing the desire is not generally consummated so rapidly as in the 

 male, with whom seminal ejaculation is accomplished in a few 

 minutes or even less. The culminating point in the female 

 orgasm occurs sUghtly after that of the male, and is said to be 

 marked by the expulsion of mucus (Kristeller's mucous strands) 

 through the os uteri. The mucus is then partly withdrawn into 

 the uterus along with the semen. Coition sometimes takes place 

 without the orgasm in the female being completed or even without 

 its occurring at all, but this is abnormal, and such coitions are apt 

 to be sterile, probably because the orgasm may be an essential 

 factor in bringing about ovulation (or the release of the ova). 



Fig. 24. — Diagram illustrating wave-like movement of swimming 

 spermatozoon. (From Nagel.) 



There is definite evidence that in some animals (rabbit, ferret, 

 cat) ovulation is a reflex act, for it does not take place without 

 coition. In man coition is normally performed ventrally, but it 

 is uncertain at what stage in evolutionary history this position 

 was first adopted. 



As already mentioned the hymen of the virgin is usually 

 broken at the first coition, before which it normally remains 

 intact. Occasionally the hymen is of so elastic and yielding a 

 nature that it remains unbroken at coition. Impregnation has 

 been known to take place without actual penetration having 

 occurred, the mobility of the spermatozoa being such as to render 

 this possible after imperfect coition, but such cases are very 

 unusual. 



The number of human spermatozoa usually ejaculated at one 

 time lias been estimated at 226 millions, whereas in man only one 

 ovum is usually discharged at ovulation (sometimes two, rarely 

 three and very occasionally more). The spermatozoa make their 



