It is also a remarkable fact that very often the two sides of the body are not alike in their markings, appearing as if formed of the union, on the median line, of the right and left halves of two individuals. Thus it may happen, in annulate forms, that some of the annuli are broken exactly in the mid-dorsal and mid-ventral lines, and that the halves do not correspond in number on the two sides. In the handsome South American _Lachesis alternatus_, which derives its specific name from the two series of large C-shaped, dark, light-edged markings which adorn its back, these markings are not always alternating, as is the rule; but some may lie opposite to each other and back to back, this being due to the fact that the numbers of the markings do not correspond on the two sides. In one specimen I count twenty-four of these markings on the left side, and twenty-seven on the right. This shows that great importance cannot be attached to the number of the markings, for systematic purposes. In fact, in some Coral-snakes, _Elaps fulvius_ for instance, the number of annuli may vary from twelve to fifty-two, with every gradation between the extremes. The bilateral asymmetry to which we have alluded produces the chess-board arrangement of the ventral spots in many snakes. Among the markings which call for investigation as to their meaning, we must allude to the presence, in some Colubrids, of a small, light, dark-edged spot, or of a pair of light dots close together, in the middle of the parietal shields or on each side of the suture between these shields, which correspond in their position to the parietal organ of many Lizards. May not this marking be in some way correlated with sensory organs, like the apical pits on the scales of the body? And what is the explanation of such bizarre signs as the spectacle or the eye-spot on the hood of the Indian Cobra? At present it is as inexplicable as the lugubrious emblem on the thorax of the Death's-head Moth. It cannot be suggested that it is a warning mark intended to terrify intruders, for when the Cobra is at rest the hood is folded, and the characteristic marking is not displayed; whilst as soon as it is aroused, and the hood expanded, it faces its enemy in such a way that the spectacle, or ocellus, is not to be seen.