This is an important point to make certain of in settling any doubtful features in the nervous supply of the lateral line. Professor Semper[231], with whom as dealing with Elasmobranchii we are more directly concerned, makes the following statement: "At the time when at the front end the lateral nerve has already completely separated itself from the ectoderm, and is situated amongst the muscles, it still lies in the middle of the body close to the ectoderm, and at the hind end of the body is not yet completely segmented off (abgegliedert) from the ectoderm." Although the last sentence of this quotation may seem to be opposed to my statements, yet it appears to me probable that Professor Semper has merely seen the lateral nerve partially enclosed in the ectoderm. This position of the nerve no doubt affords a _presumption, but only a presumption_, in favour of a direct origin of the lateral nerve from the ectoderm; but against this interpretation of it are the following facts: Footnote 231: _Loc. cit._ p. 398. (1) That the front part of the lateral line is undoubtedly supplied by branches which arise in the ordinary way from the intestinal branch of the vagus; and we should not expect to find part of the lateral line supplied by nerves which originate in one way, and the remainder supplied by a nerve having a completely different and abnormal mode of origin. (2) The growth of the lateral line is quite independent of that of the lateral nerve: the latter arises subsequently to the lateral line, and, so far as is shewn by the inconclusive observation of my earliest stage, as an offshoot from the intestinal branch of the vagus; and though it grows along at first in close contact with the lateral line, yet it never presents, so far as I have seen, any indubitable indication of becoming split off from this, or of fusing with it. (3) The fact that the cranial representatives of the lateral line are supplied with nerves which originate in the normal way[232], affords a strong argument in favour of the lateral line receiving an ordinary nerve-supply. Footnote 232: Götte extends his statements about the lateral nerve to the nerves supplying the mucous canals in the head; but my observations appear to me, as far as Elasmobranchii are concerned, nearly conclusive against such a derivation of the nerves in the head. Considering all these facts, I am led to the conclusion _that the lateral nerve in Elasmobranchii arises as a branch of the vagus, and not as a direct product of the external epiblast_.