Answer:
For a contraction to occur there must first be a stimulation of the muscle in the form of an impulse (action potential) from a motor neuron (nerve that connects to muscle). Note that one motor neuron does not stimulate the entire muscle but only a number of muscle fibres within a muscle.
Explanation:
The answer is macrophages. They either actively invade these leukocytes or are phagocytosed, divide in the cells and cause lysis. The promastigotes that invade these leucocytes are transformed into amastigotes in the macrophages. These amastigotes continue attacking other healthy macrophages while others migrate to the mid gut.
The first one with the boxing crab and anemone is mutualism.
The second one with the dog and flea is parasitism.
