This slide shows a
stained cross section through the upper pharyngeal region of the lancelet Amphioxus). Observe the dorsal fin supported by a fin ray. Note the conspicuous myomeres (muscle blocks) that are separated by myosepta. Above the prominent notochord is the hollow dorsal nerve cord. The two-layered skin of the lancelet is composed of an outer epidermis of simple columnar epithelium and an inner dermis of gelatinous connective tissue.