Gidley, Science, n. s., 36:285-286, August 30, 1912.

The order Lagomorpha is old in the geological sense; fossilized bones and teeth of both pikas and rabbits are known from deposits of Oligocene age and even at that early time the structural features distinguishing these animals from other orders were well developed.

A noteworthy character of the order is the presence of four upper incisor teeth (instead of only two as in the Rodentia); also, the fibula is ankylosed to the tibia and articulates with the calcaneum. Each of the first upper incisors has a longitudinal groove on its anterior face.

All lagomorphs are herbivorous. They eat principally leaves and non-woody stems although the bark of sprouts and bushes is taken as second choice by rabbits and hares.

Correlation of structure and function is well illustrated among the lagomorphs by the means which the different species employ to detect and escape from their enemies. A gradient series is evident in which the pikas and jack rabbits are the extremes. The black-tailed jack rabbit, for example, in relation to size of the entire animal, has the longest ears and longest hind legs. This kind of lagomorph takes alarm when an enemy, for example, a coyote, is yet a long way off. The jack rabbit seeks safety in running; even when being overtaken by a pursuer that is close behind, the jack rabbit still relies on its running ability instead of entering thick brush or a hole in the ground where its larger-sized pursuer would be unable to follow. A cottontail has shorter ears and shorter hind legs. It allows the enemy to approach more closely than the jack rabbit does before running, and then, although relying in some measure on its running ability for escape, flees to a burrow or thicket for safety from its pursuer. The brush rabbit with ears and hind legs shorter than those of the cottontail seldom if ever ventures farther than 45 feet away from the edge of dense cover. After an enemy is near, the brush rabbit has merely to scamper back into the brush. Still shorter of ear and hind leg is the pigmy rabbit which ventures outside its burrow to feed only among the tall and closely-spaced bushes of sagebrush among which its burrow is dug. Detection of the slightest movement of an enemy on the opposite side of the bush sends the pigmy rabbit, in one or a few jumps, into the mouth of its burrow and, if need be, below ground. The pika, with the shortest ears and legs of all, lives in the rock slides and has to do little more than drop off the top of a rock into a space between the broken rocks when an enemy is detected near enough to the pika to have a chance of seizing it.

The number of molts in a year, depending on the kind of lagomorph, varies in adults from one (according to Nelson, 1909:31) in the cottontails (genus Sylvilagus) to as many as three (according to Lyman, 1943, and Severaid, 1945) in the varying hare (Lepus americanus). Difficulties that I have experienced in attempting to account for the variations in color and wear of the pelage of the pika, Ochotona princeps, on the basis of two molts per year, make me wonder if it, too, has three molts. Lepus townsendii certainly has at least two molts per year.

Key to Families and Genera of Lagomorpha

• 1. Hind legs scarcely larger than forelegs; hind foot less than 40; nasals widest anteriorly; no supraorbital process on frontal; five cheek teeth on each side above
• Family Ochotonidae, Genus Ochotona, p. 125
• 1´. Hind legs notably larger than forelegs; hind foot more than 40; nasals widest posteriorly; supraorbital process on frontal; six cheek teeth on each side above
• Family Leporidae, p.