[Illustration: FIG. 21. Plantar views of right hind foot (male at left, female at right) of _T. o. ornata_ (× 1), showing sexual dimorphism in the shape and position of the first toe. The widened, thickened, and inturned terminal phalanx on the first toe of the male is used to grasp the female before and during coitus.] SEXUAL DIMORPHISM Differences between adult males and females of _T. ornata_ have been mentioned in several places in the preceding discussion of growth and development. Several sexual characteristics--greater preanal length, thickened base of the tail, slightly concave plastron, and smaller bulk--are found also in males of many other kinds of emyid turtles. From females, males of _T. ornata_ are most easily distinguished by the bright colors of their eyes, heads, and antebrachial scales. An additional, distinctive characteristic of males is the highly modified hind foot. The first toe is greatly thickened and widened; when the foot is extended, the first toe is held in a horizontal plane nearly at right angles to the medial edge of the plantar surface (Fig. 21). The hind foot of females is unmodified in this respect. Males tend to have heavier, more muscular hind legs than females. The bright colors of males are maintained throughout the year and do not become more intense in the breeding season. Males of _T. o. luteola_ become melanistic in old age whereas males of the subspecies _ornata_ do not. In old males of _luteola_ the skin becomes dark gray, bluish, or nearly black and much of the bright orange or red of the antebrachial scales and the green of the head is obliterated; the iris may also darken but in most specimens it retains some red. Females of _luteola_ tend also to darken somewhat in old age but not so much as males; females of _ornata_ do not. Table 4 summarizes the more important secondary sexual characters of _T. ornata_.