a. [f. mod.L. Acrania, sb. pl., applied by Haeckel to the lowest type of Vertebrata, represented by the Amphioxus or Lancelot: see prec.]
1870. Rolleston, Anim. Life, 32. In all Vertebrata, with the exception of the Amphioxus, which is hence called ‘Acranial,’ the neural canal widens considerably in the anterior region of the body.
1878. Bell, Gegenbauer’s Elem. Comp. Anat., 444. The indifferent stage in which the head is found in the Acrania makes it impossible to distinguish any distinct cephalic skeleton.
