Abortion or Manslaughter?

P calls W, a pathologist, to give his medical opinion that based on his examination of slides of fetal tissue, the fetus drew a breath of air before it died. Is D entitled to cross-examine Wabout his qualifications as a pathologist before he gives his opinion? What is the material issue to which such examination would be directed? Would D be entitled, before the doctor gave his opinion, to call witnesses of his own to prove that the doctor is not qualified?