The rule of embryonic development was given by

Assertion : Senescence is the time when age associated defects are manifested.

Reason : Certain genes may be undergoing sequential switching on and off during one's life.

Embryologists can presume the future organs of the embryo in

Sperm's acrosome has

$A$ : Failure of testes to descend into the scrotum causes sterility in man.
$R$ : Higher internal body temperature is not suitable for sperm development.