Final answer:
The ball of jelly on the left eye of a mantis refers to its compound eye, which assists in detecting movement for hunting and camouflage.
Step-by-step explanation:
The ball of jelly on the left eye of a mantis is likely a reference to the compound eye structure that many insects, including mantises, possess. These eyes consist of numerous tiny lenses and are exceptionally good at detecting movement, helping the mantis to spot its prey and predators.
In the context of camouflage, like the dead leaf mantis in Figure 12.8.2, these eyes can help them remain inconspicuous while hunting or when avoiding predators by blending in with their surroundings.