The tails of the turtles, like those of the horned lizards (Phrynosoma and Moloch), are almost too small and insignificant, as reptile tails go, to warrant discussion here, being reduced to but a relatively small fraction of the total length—usually less than thirty per cent.
Many reptiles vibrate their tails when disturbed, but none are better equipped by nature to capitalize this tendency than the venomous rattlers, which, unlike most other poisonous snakes, usually warn their would-be victims before attempting to molest them. The snakes of the genus Coluber, known generally as the racers, are unusually nervous and will frequently vibrate the tail when disturbed. Exhibiting this same tendency, a small lizard, the common spiny-swift of central Kansas (Sceloporus undulatus thayerii), reminds one of a pleased dog as it quivers its little tail in anticipation of food.
The Old World chameleons have a prehensile or clinging type of tail somewhat similar to that of the opossum. This is a rather unique development among the reptiles, although it is said also to have taken place in a rare iguanid lizard of the West Indies which is known to scientists as Xiphocercus valencienni.
Inhabiting the southwestern United States and the Mexican mainland are the poisonous gila monsters, which have large, rounded tails. These are covered with beadlike scales and are said to act as reservoirs for food, fat being stored in them during times of prosperity and used from them during the periods of inactivity known as hibernation and aestivation.
The tails of many lizards including those of various geckos, skinks, and "glass-snakes," are very delicate and consequently fragile and easily broken. This feature often spares the life of these animals, for an enemy in pursuit, having succeeded in grasping the tail alone, usually gets a section of just that, and nothing more. If the tail of a skink is injured in any way, so that it starts to come off, the section back of the injury is very apt to be shed whether it is firmly held or not. I have personally observed this phenomenon in the field in the case of an adult Sonoran skink (Eumeces obsoletus), which severed its long tail by a series of quick muscular contractions after a slight cut had been made accidentally near the base. After the tail has been broken, the wound heals readily and new or regenerated tissue grows. The part that develops in this manner, although not as long as the section lost, often becomes fully as long or even longer than the remaining stub of the original tail. In many regions various adult skinks and, in fact, certain other lizards, too, nearly all have regenerated or incomplete tails, and middle-sized or even young examples frequently show this state as well. Regeneration often produces freaks, as many scientists have shown, and extra tails are sometimes added after an injury. Two tails are found rather frequently in lizards, but three-tailed examples, although occasionally seen, are decidedly rare.
Amphibians have been divided into three main groups, the tailed and the tailless sections, and the section comprised of the little-known, wormlike caecilians which we need not consider. The tailed amphibians do not undergo complete change in outline between the young and adult stages, but are much the same in general appearance throughout their existence, whereas the tailless amphibians, named with reference to the adult anatomy, have a primary or tadpole stage in which the tail is present as in the other group and a secondary or adult stage in which the tail is lost. All degrees of transition between these two extremes may be seen in a carefully selected developmental series of our common frogs and toads. It seems appropriate at this point to call attention to the fact that in certain salamanders, particularly in some plethodontids, the base of the tail is constricted for loss at times of danger, thus serving the same protective purpose as the tails of the lizards mentioned above.
Fishes are specialized for aquatic life and possess flattened, rudder-like tails that aid in swimming as do similar tails in other groups. The fish-tail, although essentially constant in function and compression, is subjected to numerous variations in detail and outline. Therefore, the structure and appearance of the tail has been deemed of great importance in the classification of the group.