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Show 1895.] HYDEACHNID POUND IN COENWALL. 183 some Oribatidae, e. g. Cepheus latus, which, as it eats partly solid has a wider oesophagus and pharynx, and shows more plainly, and there the principle is practically the same; although, to admit of the larger extention, there are some muscles for depressing the floor of the pharynx, and there are undoubtedly ring-muscles on the oesophagus. In the Gamasidae, although the principle is somewhat similar, I have found considerable differences of detail, and even of more than detail 2 The mode in which the dilatores pharyngis muscles are attached to the roof of the pharynx in Thyas petrophilus is particularly beautiful; I have not seen anything like it drawn or described in other Acarina to m y recollection; therefore I have figured it (fig. 27). The muscles of the Acarina are attached to their poiut of insertion either directly or, more commonly, by means of tendons, which are often yavy long. Where several separate muscles, or a fasciculus of muscles, are inserted together, their separate tendons usually join some little distance from the point of insertion and form a common tendon ; in the present instance, however, the dilatores pharyngis are mostly strap-like muscles passing diagonally from where they arise to their insertion; each muscle appears quite separate, each may possibly be a band of muscles attached by their edges; but it has not any appearance of being so, nor does it differ from the appearance of other strap-like muscles which are each attached by a single tendon. In the present instance, however, each muscle widens out a little towards its inserted end, and that end is attached to the point, or rather line of insertion, by four or more separate tendons varying from about '005 m m . to about -015 m m . in length and which diverge a little, thus giving the muscle a grasp over a large surface of the pharyngeal wall which it has to raise; a similar arrangement is found in some of the other broad muscles of the present species, but not so well developed. These dilatores pharyngis muscles are innervated by a special azygous nerve (figs. 20, 23, 27, nph.) arising from the supra-oesophageal portion of the brain (or central ganglion) almost immediately above the oesophagus, and running parallel to and above the oesophagus, until the pharyngeal muscles are reached, when it divides, sending off a twig to each dilator muscle. The whole course of this nerve may be beautifully seen in one or two of m y preparations. I call it the pharyngeal nerve. I do not find that Schaub says where his phanyngeal muscles are innervated from, but Henkin (in Trombidium) draws and mentions this nerve, but does not appear to have traced it to its origin. Croneberg in his fig. 16, Eylais, draws two paired nerves, which he letters " n, n "; they come, so far as I can judge, from the supra-cesophageal portion of the brain; each divides into two equal branches very near its origin. In the explanation of his fig. 16, Croneberg says that "b,b" are the nerves going to the pharynx and mandibles; but there is not any 1 " On the Variations in the Internal Anatomy of the Gamasinse, &c." Trans. Linn. Soc, Zool. vol. v. pt. 9, p. 310, pi. 73, |