Dohrn, op. cit.
See pp. [120] and [135]. Willey, Amphioxus and the Ancestry of the Vertebrates, New York, 1894, pp. 30, 31.
Beard, Anat. Anz. ix. 1894, p. 485.
Newton Parker, op. cit. p. 135.
Giacomini, quoted by Swale Vincent, Journ. Anat. and Phys. xxxviii. 1903, p. 41.