Funnel shaped ciliated pits on the ventral side of kidney of Frog

1. Ostia
2. Nephrostomes
3. Nephridiopores
4. Coelomostomes

In frog, there are few ciliated funnels, the nephrostomes, are situated on the ventral surface of the kidney to collect the excretory matter from the coelom and pour it into the renal vein. The nephrostome is the funnel-like component of a metanephridium. It is always oriented towards the coelom.

So the correct answer is 'Nephrostomes'.