By a simple modification, the open pit becomes a solid ectodermal ingrowth, just as in Teleostean fishes the hollow medullary tube, or the auditory pit of other vertebrate embryos, is formed at first as a solid cord of cells, which acquires a cavity secondarily.
He has shown that, as in the Crossopterygian and Chondrostean ganoid fishes, there co., are two clavicular elements on each side; the lower corresponds to the clavicle of reptiles and higher vertebrates, whilst the upper corresponds to the clavicle of teleostean fishes, and has been named by him "cleithrum."
This type of caudal fin must be regarded as secondary, the Gadidae being, no doubt, derived from fishes in which the homocercal fin of the typical Teleostean had been lost.