An acquired trait is experienced by an individual during his life time. It involves changes in non-reproductive tissues (or somatic cells), which cannot be passed on to the germ cells or progeny.

please explain the above lines . 

what are the non reproductive tissues and what are the changes which do not pass on to the progeny ?

The body has two types of tissue based on genetic content. The somatic tissue consists of all the tissue in the body other than the tissue where the gametes or sex cells are found. This includes your hair, skin, stomach, lungs, heart, bones, limbs etc. The reproductive tissue is the gonads, which store the gametes or sex cells. The gonads in the males are the testes and in the female they are the ovaries. The sex cells of the male are the sperm and the sex cells of the female are the ova. A trait is any morphological, physiological or functional characteristic that is encoded in the DNA and expressed in a person, for example height, ability to roll the tongue or excess production of a certain hormone. Acquired traits are the changes that occur in the somatic tissue of a person during his lifetime, which means that the changes that occur in his own body, for example development of big muscles due to working out will not be passed on to his children, because these changes have not occurred in the DNA sequence of the sex cells. Only the changes occurring in the DNA of the sex cells will be passed on to the progeny, because that is the only DNA that is passed on after fertilization.