. Amphioxus and the ancestry of the vertebrates. Amphioxus; Sea squirts; Hemichordata. 248 THE PROTOCHORDATA. wall of the proboscis known as the proboscis-pore. In B. Kowalevskii this pore lies asymmetrically to the left of the dorsal middle line (Fig. 115), while in B. Kupjferi a corresponding opening occurs to the right of the middle line, so that in this species there are two proboscis- pores constituting a sym- metrical pair. The left proboscis-pore of Balanoglossus is obvi- ously to be compared with "i-fJ*-* the praeoral pit of Amphi-. oxus. The collar-cavities also open to the exter
. Amphioxus and the ancestry of the vertebrates. Amphioxus; Sea squirts; Hemichordata. 248 THE PROTOCHORDATA. wall of the proboscis known as the proboscis-pore. In B. Kowalevskii this pore lies asymmetrically to the left of the dorsal middle line (Fig. 115), while in B. Kupjferi a corresponding opening occurs to the right of the middle line, so that in this species there are two proboscis- pores constituting a sym- metrical pair. The left proboscis-pore of Balanoglossus is obvi- ously to be compared with "i-fJ*-* the praeoral pit of Amphi-. oxus. The collar-cavities also open to the exterior by pores, one on each side underneath the dorsal pos- terior free fold of the collar, and on a level with the opening of the first gill-slit. These are the funnel-shaped collarporcs. Spengel states that water is taken in through the collar-pores into the cavity of the collar in order to swell the latter up, so that it may serve as an accessory organ of locomotion in so far as an alternate inflation and collapse of the collar would assist the animal in its slow burrowings in the sand. Fig. 117. — Diagrammatic horizontal section througii an embryo of Balanoglos- sus (type of the direct development), to show the origin of the body-cavities as archenteric pouches. (After Bateson.) ap. Tuft of cilia at the apical pole (indication of an apical plate), bc^. Probos- cis-cavity, bc^. Collar-cavities, cij^. Trunk- cavities, cb. Circular band of Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Willey, Arthur, 1867-. New York, London, Macmillan
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