. Amphioxus and the ancestry of the vertebrates. Amphioxus; Sea squirts; Hemichordata. i8 ANATOMY OF AMPHIOXUS. the buccal cartilages. As pointed out by Johannes Miiller, they are not to be compared with the jaw-apparatus, nor to the hyoid or tongue- bone of the jaw-bearing Vertebrates, but they belong to the same cate- gory as the mouth-carti- lages of the Cyclostome fishes (which possess a hyoid cartilage in addi- tion) and the labial car- tilages of Selachians (sharks). The absence of paired. auditory organ has been Fig. 3. — Anterior portion of body of young transparent individual. (After
. Amphioxus and the ancestry of the vertebrates. Amphioxus; Sea squirts; Hemichordata. i8 ANATOMY OF AMPHIOXUS. the buccal cartilages. As pointed out by Johannes Miiller, they are not to be compared with the jaw-apparatus, nor to the hyoid or tongue- bone of the jaw-bearing Vertebrates, but they belong to the same cate- gory as the mouth-carti- lages of the Cyclostome fishes (which possess a hyoid cartilage in addi- tion) and the labial car- tilages of Selachians (sharks). The absence of paired. auditory organ has been Fig. 3. — Anterior portion of body of young transparent individual. (After J. MiJLLER, slightly altered.) ck. Notochord. ci. Buccal cirri, e. Eye- spot, etid. Endostyle. />-. Fin-rays lying in the fin-chambers. ' Gill-slits; the skeletal Syes and of any rods of the gill-bars are indicated by blaek lines. nt. Spinal cord, with pigment granules near its base. ?-.(!. Downgrowth from right aorta lying mentioned aboVC. There to the right of vel. the velum; with velar ten- . tacles projecting back into pharynx. w.(>. Riid- ^S, no\ve\er, a median erorgan; ciliated epithelial tracts on inner ^yj^j^j., consists of a surface 01 oral hood. ^ comparatively large un- paired pigment spot lying at the anterior extremitj- of the dorsal nerve-tube.* A row of similar, but much smaller, masses of pigment lie along the floor of the spinal canal, commencing some distance behind the eye (Fig. 3). Immediately above and be- hind the eye-spot is a small f™: ^^^""^ J; ^i^ller.) The -' ^ basal pieces he end to end in the mar- pit in the body-wall reaching gin of oral hood, and each basai piece sends up an axial process into the from the outer surface of the corresponding buccal cirrus. * The eye-spot has been observed to he sometimes broken up into two pigment masses. (See Ayeks, No. 105 bibliog.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance
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