In specimens of a very much later period (Pl. 23, fig. I) the proximal portions of the outgrowth are unquestionably continuous with each other, though their actual junctions with the spinal cord are very limited in extent. The fact of this continuity at a later period is strongly in favour of the view that the posterior branches of the spinal nerves arise from the first as a continuous outgrowth of the spinal cord, from which a series of distal processes take their origin. I have, however, failed to demonstrate this point absolutely. The processes, which we may call the nerve-rudiments, are, as appears from the later stages, equal in number to the muscle-plates. It may be pointed out, as must have been gathered from the description above, that the nerve-rudiments have at this stage but one point of attachment to the spinal cord, and that this one corresponds with the dorsal or posterior root of the adult nerve. The rudiments are, in fact, those of the posterior root only. The next or second stage in the formation of these structures to which I would call attention occurs at about the time when three to five visceral clefts are present. The disappearance from the notochord in the anterior extremity of the body of a special central area rich in protoplasm serves as an excellent guide to the commencement of this epoch. Its investigation is beset with far greater difficulties than the previous one. This is owing partly to the fact that a number of connective-tissue cells, which are only with great difficulty to be distinguished from the cells which compose the spinal nerves, make their appearance around the latter, and partly to the fact that the attachment of the spinal nerves to the neural canal becomes much smaller, and therefore more difficult to study. Fortunately, however, in _Torpedo_ these peculiar features are not present to nearly the same extent as in _Pristiurus_ and _Scyllium_. The connective-tissue cells, though they appear earlier in _Torpedo_ than in the two other genera, are much less densely packed, and the large attachment of the nerves to the neural canal is retained for a longer period. Under these circumstances I consider it better, before proceeding with this stage, to give a description of the occurrences in _Torpedo_, and after that to return to the history of the nerves in the genera _Pristiurus_ and _Scyllium_. _The development of the Spinal Nerves in Torpedo._ The youngest _Torpedo_-embryo in which I have found traces of the spinal nerves belongs to the earliest part of what I called the second stage.