Section 3. Figure 1, Sheet 19, Shows the General Anatomy of

Amphioxus. We recognise four important points of resemblance to the earlier phases of the higher and the permanent structure of the lower members of the vertebrata, and it is these that justify the inclusion of amphioxus in this volume. In the first place there is the--

-Notochord_. In the next, just above it (at s.c.) we find--

-A Dorsal Tubular Nervous Axis_, the spinal cord. Thirdly, the pharynx (ph.) is perforated by--

-Respiratory Slits_, though these, instead of being straight slashes, are modified from a U-shape [slant very much forward and are much more numerous than in any true vertebrate.]. -And-, Fourthly, there is, as we shall see, a--

-Vertebrate Type of Circulation_. [And finally the body-wall muscles are divided into--]