second plexus (_m_), where the inner antennular nerve and ophthalmic nerve cross over the outer antennular nerve. I have called the nerves (_dd_, _ee_) splanchnic and supra-splanchnic, from their course and apparent function in supplying the viscera. In the descriptions of the nervous system of other Crustaceans I can find nothing analogous to my great splanchnic nerve (_dd_); the so-called supra-splanchnic nerves (_ee_), which arise from the circa-œsophageal chord, seem to be the analogues of the ordinary splanchnic nerves, though these latter are always described as uniting into a single medial branch. The plexus (_d′_) is the cervical ganglion of M. Martin St. Ange,[40] who has likewise indicated the course of my splanchnic and supra-splanchnic nerves; but the plexus, when viewed as a transparent object, hardly appears to me to be ganglionic in its nature. In my former volume on the Lepadidæ, I quite misunderstood the course of these splanchnic nerves. [40] 'Mémoire sur l'Organisation des Cirripèdes,' p. 19. From the commissure between the two supra-œsophageal ganglions, a straight chord (Pl. 27, fig. 1, _g_) arises, which terminates in a small ganglion (C), barely exhibiting traces of being formed of two laterally confluent ganglions. This is the ophthalmic ganglion. The chord connecting it with the two supra-œsophageal ganglions is accompanied by a small nerve (_h_) which runs on to the muscles round the adductor scutorum muscle; the chord is encased by much fibrous tissue, and its dissection is thereby rendered difficult. From the ophthalmic ganglion, on each side, a nerve (_i_) goes forth and crosses the antennular nerve; these, if I could have traced them, would have been found to run, as may be safely inferred from what is known in _Balanus tintinnabulum_, to a pair (D, D) of eyes.