94 LIVESTOCK ON THE FARM 



such time as they may be needed. This is at the time of 

 service when the sperm cells of the male are deposited in the 

 vagina of the female. They are usually deposited in large 

 numbers but only one is needed to fertiUze an egg. These 

 sperm cells look a little like tadpoles. They have tails by 

 means of which they can move and thus get into the opening 

 through the neck into the womb and there meet the egg cell 

 from the female. When these two meet and the conditions 

 are right they combine and form the new individual. This 

 then develops from two cells which unite and make one cell 

 and then this grows by cell division. Next there are two cells, 

 then four, eight, sixteen, thirty-two, sixty-four, etc. 



At first this new individual lives upon the food contained 

 in the egg. After a very short time, however, it attaches itself 

 to the wall of the womb and absorbs food from it. The 

 afterbirth or placenta is only the connection between the 

 foetus and the womb of the dam. 



The fcBtus or new individual is an entirelj'' independent 

 individual. It has its own life, metabolism, blood circulation, 

 etc. But it cannot use its lungs to purify air for its own 

 metabolism, consequently, it sends its blood stream by means 

 of the navel cord to the placenta or afterbirth which surrounds 

 the entire foetus and attaches to the interior of the womb. 

 Here the blood is spread out thinly, as in the lung of the 

 animal after birth, and is purified. The impurities are taken 

 out and oxygen is taken from the blood stream of the dam and 

 put into the blood stream of the foetus. These materials are 

 passed through the walls of adjoining blood vessels, those of 

 the dam and of the foetus. Thus there is no direct blood 

 connection between the dam and its offspring. 



As the foetus grows the womb must enlarge. At birth when 

 the foetus has been expelled the afterbirth is also expelled and 

 the womb then again contracts to its normal size. The 

 foetus is expelled by means of the contraction of the muscles 

 of the womb and of the abdomen. 



HEREDITY 



A new animal has its inception or beginning when the sperm 

 cell of the male and the egg cell of the female unite. This is 



