Why are Birds and Reptiles with abundant yolk sac polyspermic?
My professor says that


  The yolk sac is not connected to the mechanism of polyspermy or
  monospermy. [Amount of yolk inside the oocyte is then again.]  The
  oocytes of reptiles and birds are yolk rich  - polylecithal  for instance.


where
lecithal = yolk containing and some pieces of information about here.