In the course of studies on the morphology of the head in vertebrates I have been much interested in the interpretation of the vagus. The explanation of this as a collection of several true branchial nerves (Johnston, 1905) required some special modification to fit the case of the myxinoids, in which according to earlier writers the I X and X nerves are united. This condition was met by supposing that the process of collecting the branchial nerves, as it proceeded from behind forward, went a

more »

... p further in myxinoids than it has in gnathostomes, and so carried the whole series of (IX and X) branchial nerves into a single complex. This view has always seemed to me somewhat strained, but the facts necessary for a more natural explanation were not available until later. The facts referred to concern the disappearance of gills in the cephalic part of the series. This, indeed, was referred to in my paper on the morphology of the head (1905, p. 191), but the meager account by Price (1896) did not lead me to see its bearing on the question of the 1X nerve, especially since Price expressed the opinion that as many as twenty-three or twenty-four gills had disappeared. My remarks on the disappearance of gills in Bdellostoma have been seriously criticised by Stockard (1906, p. 487), who says: "Price, working with a limited supply of material, made the mistake of supposing that a great number of gill pouches appear during development, possibly *Neurological Studies, University of Minnesota, No. 7.