In fish and
many invertebrates, respiration takes place through the gills.
breath passively through their spiracles (special openings in the exoskeleton)
and the air reaches the body by means of a series of smaller and smaller pipes
called 'trachaea' when their diameter is relatively large and 'tracheoles' when
their diameter is very small.
occurs under the control of the autonomic nervous system from parts of the
brain stem, the medulla oblongata and the pons.