At 21 weeks the best visual is an ultrasound picture (they all look similar). They are developed and moving, and so look like hairless miniature curled up babies.
By this point your baby has probably reached about ten inches or a little more and should be around three and a half pounds. Baby has developed eyelids and eyebrows this week.
At 21 weeks along your baby looks like a baby, you can distinquish its arms, legs, eyes ears etc, The baby's skin is transparent and very thin however it is there.