The wing is made of a web of skin extended on the enormously elongated outermost finger. The long tail served for balancing and steering. The Pterodactyls varied from the size of sparrows to a wing-span of fifteen feet--the largest flying creatures.] [Illustration: _From Knipe's "Nebula to Man."_ PARIASAURUS: AN EXTINCT VEGETARIAN TRIASSIC REPTILE Total length about 9 feet. (Remains found in Cape Colony, South Africa.)] [Illustration: _From Knipe's "Nebula to Man."_ TRICERATOPS: A HUGE EXTINCT REPTILE (From remains found in Cretaceous strata of Wyoming, U.S.A.) This Dinosaur, about the size of a large rhinoceros, had a huge three-horned skull with a remarkable bony collar over the neck. But, as in many other cases, its brain was so small that it could have passed down the spinal canal in which the spinal cord lies. Perhaps this partly accounts for the extinction of giant reptiles.] [Illustration: _Photo: "Daily Mail."_ THE DUCKMOLE OR DUCK-BILLED PLATYPUS OF AUSTRALIA The Duckmole or Duck-billed Platypus of Australia is a survivor of the most primitive mammals. It harks back to reptiles, e.g. in being an egg-layer, in having comparatively large eggs, and in being imperfectly warm-blooded. It swims well and feeds on small water-animals. It can also burrow.] Evolution of the Voice The first use of the voice was probably that indicated by our frogs and toads--it serves as a sex-call. That is the meaning of the trumpeting with which frogs herald the spring, and it is often only in the males that the voice is well developed. But if we look forward, past Amphibians altogether, we find the voice becoming a maternal call helping to secure the safety of the young--a use very obvious when young birds squat motionless at the sound of the parent's danger-note. Later on, probably, the voice became an infantile call, as when the unhatched crocodile pipes from within the deeply buried egg, signalling to the mother that it is time to be unearthed. Higher still the voice expresses emotion, as in the song of birds, often outside the limits of the breeding time. Later still, particular sounds become words, signifying particular things or feelings, such as "food," "danger," "home," "anger," and "joy." Finally words become a medium of social intercourse and as symbols help to make it possible for man to reason. Sec. 2 The Early Reptiles