Simplify the following text for a Grade 7 native English-speaking person.
Original: The two species of lizard within the genus Iguana possess a dewlap , a row of spines running down their back to their tail , and a third `` eye '' on their head .
Simplified: The two species of lizard both have a dewlap , a row of spines running down their back to their tail , and a third eye on their head .