You should read pages 558-559 carefully, perhaps making an outline to understand some of the possible mechanisms that lead to speciation. Again, you should be familiar with these. The third species separated from common ancestors WAY WAY back in evolutionary time. The interfaces with this third species are probably ruled by competitive exlusion rather than parapatric speciation. Panel c similarly shows sympatric species, but again, these two species are not the result of a recent sympatric speciation event.
Allopatric speciation is the easiest to understand, particularly on oceanic islands.
For those of you who went to Bermuda, you learned about several endemic species. There is a similar situation with drosophiloid insects on Hawaii. Find the second paragraph on page 561. Starting with the third sentence, read the rest of the paragraph repeatedly until you understand it fully. Until you understand these critical sentences, you cannot appreciate the mechanism of speciation.