1895.] HTDEACHNID FOTTtTD IN COENWALL. 183 



some Oribatidse, e. g. Ceplieus ?a<M5, which, as it eats partly solid food, 

 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 '. 



The mode in which the dilatox'es pharyngis muscles are attached 

 to tlie roof of the pharynx in Thyas petrophilus is particularly 

 beautiful ; I have not seen anything like it drawn or described in 

 other Acarina to my recollection ; therefore I have figm-ed it 

 (fig. 27). The muscles of the Acarina are attached to their point 

 of insertion either directly or, more commonly, by means of 

 tendons, which are often very 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 mm. to about '015 mm. 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 an'angement 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-cesophageal 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 my preparations. I call it the 

 pharyngeal nerve. 1 do not find that Schaub says where his 

 phanyngeal muscles are innervated from, but Henkin (in Trom- 

 bidium) 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-oesophageal 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 



* " On the Variations in the Internal Anatomy of the Gamasinse, &c." Trans. 

 Linn. Soc, Zool. vol. v. pt. 9, p. 310, pi. 73. 



