Rain is very scarce, but the canals supply ample water for cultivation and all other purposes.
Numerous canals intersect the district, affording ample means of irrigation.
Alkmaar is a typical North Holland town, with tree-lined canals and brightly coloured 17th-century houses.
Canals lead from Milan to the Ticino, Adda and P0.
In this order the radial canals are represented only by wide gastric pouches, and in the family Solmaridae are suppressed altogether, so that the tentacles and the festoons of the ring-canal arise directly from the stomach.