REPRODUCTION 

 H 



357 



Figure ig8. Female reproduc- 

 tive organs of the Common Dol- 

 phin with uterus and vagina in 

 section. F = annular fold [see 

 Figure igy) ; C = cervix ; H 

 = uterine horn; O = ovary. 

 {Prcraft, ig32.) 



and carry them to the uterus, are straight tubes in some species, and twisted 

 to a varying extent in others. 



The Cetacean ovaries are roughly in the same place as the testes of the 

 opposite sex, but even though they are much smaller organs, the ovaries 

 of Rorquals can be up to one foot long and can often weigh as much as 

 twenty-two pounds. On one occasion, the British whaler Balaena caught 

 an eighty-three-foot pregnant Blue Whale each of whose ovaries weighed 

 sixty-five pounds. The ovaries of Odontocetes resemble those of other 

 mammals, but Mysticetes have ovaries whose appearance is far more akin 

 to those of birds. In adolescent Mysticetes, they are fairly flat organs 

 provided ^vith a varying number of grooves, but in adults they resemble 

 an enormous bunch of grapes (Fig. 199). If one of the 'grapes', i.e. a 

 follicle with a diameter of from i J to 2 inches, is cut, a fairly transparent 

 fluid spills out, and keen eyes can often make out the ovum, a tiny spot, 

 0-I-0-2 mm. in diameter, near its inner wall - the beginnings of a future 

 colossus weighing 100 tons. 



By and large, the ovaries of most mammals are constructed on the same 

 pattern : a large number of ova, each in a follicle of its own. When a given 

 female is not in season, her follicles are 'immature' and so devoid of 

 internal moisture that the walls come into close contact with the ova 

 inside. As the follicle matures, it becomes distended by the accumulation 

 of fluid, and moves outwards to the surface of the ovary, from which it 

 begins to protrude. At the height of oestrus, the pressure in the follicle 

 becomes so great that, for instance in Fin Whales, it increases to about 

 three inches in diameter. Then its wall bursts in a definite spot, and the 

 ovum is discharged. It is subsequently caught in the funnel-shaped 

 opening of the oviduct where it may be fertilized by a spermatozoon, and 

 then travel on to the uterus. In multiparous (i.e. litter-producing) 



