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Show 1895.] HYDBACHNID FOUND IN COBNWALL. 201 between Schaub's description and Thyas petrophilus is that he shows two fine branches as springing from the optic nerve some time before the final division into two ; I find three such branches quite plainly visible in dissections. Schaub says that these branches go to sense-organs in the dorsal shield ; I have not been able to find such sense-organs in m y species, which has not the peculiar dorsal plate of Hydrodroma in which they are situated, and I have not been able to trace where the three fine branches in m y species go to : I have two or three dissections showing the whole course of the optic nerve from the brain to the eye, and showing these branches for some distance; but I have not been able to trace them to their destinations and I cannot follow them in the sections. The fourth pair of nerves from the upper ganglion is a pair of very thin nerves from near the posterior edge of the brain (fig. 20, nu.), and which lie above and between the nerves serving the fourth pair of legs and the genital nerves: these nerves are extremely fine and difficult to trace, but are certainly present; I have not succeeded iu ascertaining what organs they innervate. The pair of nerves which proceed from the level of the oesophagus, so that it is hard to say whether they are supra- or sub-oesophageal, are shown at fig. 20, np.; they are long and substantial nerves and I have sections showing them well in their entire length. Each nerve, shortly after leaving the brain, forms a ganglionic swelling and then diminishes to its former size : about halfway between the brain and its destination it sends a very small branch downward; I have not been able to trace this to its destination. Some distance from its termination the principal nerve divides dichotomously, sending one branch (np. 1) forward and upward to the palpus, aud the other (np. 2) forward and downward to the maxillary lip ; a short distance before reaching which it forms a small ganglionic swelling. This nerve is probably homologous with Schaub's nerve " ant," which he says serves the palpi and mandibles; of course this m a y be so in his species, but as the palpi are maxillary palpi and the maxillary lip in Acarina is formed of the fused maxillae, tbe distribution to palpi and maxillary lip seems more what might be expected than that to palpi and mandibles. Schaub considered that the palpi wrere innervated from the supra-cesophageal; Croneberg from the sub-oesophageal ganglion. Nalepa (in Tyroglyphus) considered that the maxillae were served by the sub-, and the maxillary palpi by the supra-cesophageal ganglion. In the present species it is, as before stated, impossible to say which ganglion the nerve belongs to. Of the nerves clearly proceeding from the sub-cesophageal part of the brain-mass there are, firstly, the four pairs of great nerves proceeding to the four pairs of legs (fig. 20, n 1, n 2, n 3, n 4) ; as to the existence and position of which all writers are agreed ; but all have hitherto described and figured them as unbranched nerves, at least no one has described any branches, although their |