The connecting link between the fish and the reptile groups is the amphibians--frogs, newts, salamanders, etc. The frog in its tadpole stage is a fish, but acquiring legs and lungs it becomes an air-breather, a land animal. Between the reptile and the bird, and having certain characteristics of both, there are at least three extinct species, known by their fossils. One of these, archaeopteryx, had the skeleton and feathers of a bird and a reptile tail composed of twenty vertebrae. Another was a flying reptile with a bird-shaped head. Reptiles (snakes, lizards, turtles, aligators, etc.) are cold-blooded, egg-laying animals. Birds retain the egg-laying characteristic of reptiles but are warm-blooded like the mammals. The latter differ from both birds and reptiles in producing their young alive and suckling them. Between the mammal and its ancestor, the reptile, but classed with the former is the duck-mole of Australia. It is an egg-laying, web-footed, duck-billed quadruped. After its young are hatched they are suckled in a sort of mammary pouch which is without nipples. Above the duck-mole, but so low in the mammal group that they are not really mammals are the marsupials (kangaroos, opossums, etc.). Their young are so immature at birth that they are for some time carried in a pouch by the mother. We have now come to the last great chasm--that between man and the other mammals. As man belongs in the same group with them the chasm is not so great in the sum of physical characters as is that between the fish and the reptile groups, or between the reptiles and the mammals. In regard to man and the higher apes the dividing line, viewed from the stand-point of descent, is vertical rather than horizontal--like that between mammals and birds. There are no species, extinct or extant, between man and the ape. It is not necessary for the proof of evolution that there should be. “Missing links” are not more required here than they are between birds and mammals which were evolved side by side from reptiles. If ten feet below the topmost bough of a tree there is another branch it is not necessary to show that there are, or have been, intermediate branches to prove that both grew from the same trunk. Missing links are required only _in the line of descent_.