100 THE VERTEBRATE OVARY AND ITS RELATIONSHIP TO REPRODUCTION 



terone. The two hormones thus work together to promote a gradual devel- 

 opment of the uterine tissue and maintain a regulated, balanced condition 

 throughout pregnancy. The placenta, through its ability to elaborate proges- 

 terone and estrogen during the latter phases of pregnancy, is an important 

 feature regulating pregnancy in some mammals. 



It should be emphasized in connection with the above statements that the 

 presence of the fertilized egg and its subsequent development in some manner 

 affects the maintenance of the corpus luteum. The mechanism by which this 

 influence is conveyed to the ovary is unknown. 



2. Gestation Periods, in Days, of Some Common Mammals* 



* Adapted from Asdell, '46; Cahalane, '47; Kenneth, '43. 



Armadillo (Dasypus novemcinctus) 150 



Bear, black (Ursiis americanus) 210 



Bear, polar (Thalarctos maritimiis) 240 



Beaver, Canadian (Castor canadensis) 94-100 



Bison (Bison bison) 276 



Cat, domestic (Felis catiis) 60 



Cattle (Bos taiirus) 282 



Chimpanzee (Pan satyrus) 250 

 Deer, Virginian (Odocoileus virginianits) 160-200 



Dog, domestic (Canis familiar is) 58-65 



Donkey, domestic (Equus asinus) 365-380 



Elephant (Elephas africanus) 641 



Elephant (Elephas indiciis) 607-641 



Elk (A Ices alces) 250 



Ferret (Putoriiis furo) 42 



Fox, arctic (Alopex lagopus) 60 



Fox, red (Vulpes vulpes and V. fulva) 52-63 



Giraffe (Giraffa camelopardalis) 450 



Goat, domestic (Capra hi reus) 140-160 



Guinea pig (Cavia porcellus) 68-71 



Horse (Equus caballus) 330-380 



Man (Homo sapiens) 270-295 



Lion (Felis leo) 106 



Lynx (Lynx canadensis) 63 



Marten, American (Martes americana) 267-280 



Mink (Mustela vison) 42-76 



Mole (Talpa europaea) 30 



Monkey, macaque (Macaca mulato) 160-179 



Mouse, house (Mus musculus) 20-21 



Opossum (Didelphis virginiana) 13 



V\g (Sus scrofa) 115-120 

 Rabbit (Lepus: Sylvilagus; Oryctolagus) 30-43 



Rats (Various species) 21-25 



Seal, fur (Callorhinus sp.) 340-350 



Sheep, domestic (Ovis aries) 144-160 



Skunk, common (Mephitis mephitis) 63 



Squirrel, red (Tamiasciurus sp.) 30-40 



