In most simple type of canal system of Porifera, water flows through which one of the following ways?

Ostia $\to$  Spongocoel $\to$  Osculum $\to$  Exterior
Ostia are the small pores on the surface of the members of porifera which opens into a big chamber like spongocoel (body cavity) where filtered water is given out through osculum (a large opening).