f 



178 PHYSIOLOGY OF FARM ANIMALS [CH. 



about sixteen times their original cubical content and come to 

 contain a yellow pigmented fat called lutein. The corpus luteum 

 thus formed persists in the dog until the close of jjseudo -pregnancy 

 or pregnancy when the luteal cells become vacuolated and shrink. 

 The corpus luteum eventually degenerates, leaving merely a scar. 

 Contemporaneously with the growth of the corpus luteum 

 the mammary glands develop both during pregnancy and during 

 pseiido-pregnanc}^ and milk secretion may occur at the end of 



Fig. 92. Fully formed corpus luteum of mouse (after 

 Sabotta from Schafer). 



each of these periods but the growth of the glands and their 

 subsequent activity are less incomplete when true gestation does 

 not take place. 



The period of gestation in the dog is about 62 days, and pseudo- 

 pregnancy may be said to last for about the same time or perhaps 

 not quite so long. It does not terminate so abruj)tly as true 

 pregnancy, and the uterus passes gradually back to the condition 

 of quiescence which is characteristic of the anoestrum^. This 



^ It is noteworthy that at the end of pseudo -pregnancy a bitcli niaj' behave 

 like one about to give birth and prepare a bed for pups. Hammond has noted 

 similar phenomena with doe rabbits wliich (exceptionally) experience psoudo- 

 pregnancy. 



