Section 7. The method of examining cross-sections is an extremely convenient one in the study of such a type as Amphioxus. The student should very carefully go over and copy the six sections on Sheet 20, comparing Figure 1 as he goes. He should do this before reading what follows. One little matter must be borne in mind. These figures are merely intended to convey the great structural ideas, and they are considerably simplified; they must not be regarded as a substitute for the examination of microscopic sections. [He will notice a number of rounded masses from the body wall. The] -For instance, the body-wall- muscles of Amphioxus are arranged in bundles bent sharply in an arrow shape, the point forward. -A number of these bundles are cut in any one section, and so the even shading of our diagrams, if they professed to be anything more than diagrams, should be broken up into masses.- These -bundles, we may mention-, are called myomeres, and they are indicated in Figure 1 by lines pointing acutely forward. [Several are consequently cut in any transverse section (Sheet 20), and these are the rounded masses he sees.] Similar myomeres, similarly situated, are found in fish, behind the head, and, less obviously, they occur with diminishing importance as the scale of the vertebrata is ascended. Section 8. If we compare the nervous system of amphioxus with that of any vertebrate, we find at once a number of striking differences. In the first place, the skeletal covering of it, the cranium and the neural arches of vertebrae, are represented only by a greatly simplified connective tissue. In the next, a simple and slight anterior dilatation alone represents the brain. A patch of black pigment anterior to this (e.s.) may or may not be what its name implies an eye-spot. There is a ciliated funnel, c.f. (Figure 1, Sheet 19), opening on the left side, which has been assumed to be olfactory in its functions, and in the mouth chamber a ciliated pit (c.p.), which may, or may not, be an organ of taste. The ventral fissure of the spinal cord is absent. The dorsal nerves are without ganglia, and do not come off in pairs, but alternately, one to the left, then one to the right, one to the left, one to the right, and so on. The ventral nerves are very short, more numerous than the dorsal, and never unite with these latter to form mixed nerves.