Why does it make sense that the autonomic nervous system controls mostly involuntary processes? ...

Answer to q. 1

Controlling some body functions clearly can only be controlled involuntarily. Processes such as
digestion and heart rate could only be controlled involuntarily. Further, the system would have to have
opposing effects. For example, the parasympathetic division stimulates digestive activity while the
sympathetic division inhibits activity. Decreasing digestive activity during involuntary responses to
stress, danger, or strenuous activity, which are controlled by the sympathetic division, is necessary for
coordination of nervous system control of organ and gland function.

Answer to q. 2

Invertebrates have neurons, although in some the dendrites and axons are not clearly differentiated.
Although there is no brain in invertebrates with nerve nets, often nerve cells may be more concentrated
in some regions. More complex invertebrates have a central nervous system and peripheral nervous
system.