<span>an organelle found in large numbers in most cells, in which the biochemical processes of respiration and energy production occur. It has a double membrane, the inner layer being folded inward to form layers (cristae). </span>
Coral reefs<span> are also being degraded by many other factors. The list of problems can seem endless: overfishing, fishing using cyanide and dynamite, pollution from sewage and agriculture, massive outbreaks of predatory starfish, invasive species, and sedimentation from poor land use practices</span>
I'm not sure how exactly you wanted this question to be answered. You're either talking about the symmetry where animals would have two legs or two arms for example and thus producing a pair of each muscle on both sides of the body, or you're refering to the development of agonistic and antaonistic muscles where each of them served a different purpose; either extending or contracting.
The nucleus intructs cells to do their activities
