This characteristic of this metre - जतौ तु वंशस्थमुदीरितं जरौ ।
It means there is वंशस्थ metre of the verse in which in every quaeter (there are twelve letters, and they) chronologically are ज set, त set, ज set and र set.
Illustration :
वरं वनं व्याघ्रगजेन्द्रसेवितं
दुमालयः पत्रफलाम्बुभोजनम् ।
तृणानि शय्या वसनं च वल्कलं
न बन्धुमध्ये धनहीनजीवनम् ।।
(Meaning: Forest used by tigers and elephants is good, house in the form of a tree is good, dinner of leaves, fruits and water is good, bed of grass (hey) and clothes made of bark of a tree is good but to live without money with brothers and relatives is no good)
In the first quarter totally there are twelve letters. These 12 letters make four trieds. Out of those four trieds in the first (व रं व) there is ज set, (नं व्याघ्र) there is त set, (ग जे न्द्र) there is ज set and in the end (से वि तं) there is र set.
This is an illustration of 'Vanshastha' metre.