one evidence, however, that I can give of my sincerity is, to undertake a matter which I believe the Society would be doing good service to microscopy if it undertook itself, but which it can hardly be expected to undertake if it does not believe in its necessity, and that is to enable English microscopists to read in their own. language one of the best modern German treatises-one which (as a deceased colleague on the Council of this Society declared) is "a mine whose treasures might occupy many workers in developing." Whilst it does not pretend to be exhaustive, it will at least serve (to put it no higher) to show how extensive a field a complete knowledge of the subject embraces, and until we are able to improve upon it, it will, I think, worthily supply the want which just twenty years since was referred to in an article in the Quarterly Journal of Microscopical Science': -" The period has not yet arrived when all those who employ the microscope methodically as a means of scientific investigation possess an intelligent comprehension of the principles on which it is constructed and the nature of its powers as an optical instrument. There is a large region beyond mere manipulation into which few apparently care to enter. The writers of our introductory treatises leave the matter pretty much as they found it. Surely the time has arrived which calls for more than this; when an optical treatise on the microscope, worthy of the name, is not only desired by the few but required for the many." When completed, the Society will be better able to judge whether I have exaggerated in what I have written. I have a strong conviction that the conclusion will be that I have not, and I have a strong hope that in the result a new departure will be made in "microscopy" in England. p. 27. On the Optical Powers of the Microscope," by P. G. Rylands, vol. vii. III.-On a Species of Acarus of the genus Cheyletus, believed to be new. By A. D. MICHAEL, F.R.M.S. (Read before the ROYAL MICROSCOPICAL SOCIETY, May 1, 1878.) PLATE VI. IN the latter part of December, 1877, being on a visit to some friends near Tamworth, Warwickshire, I found, by sweeping the walls of their beer-cellar, a tolerably plentiful supply of that interesting and beautiful acarid Glyciphagus palmifer, which had not before been found in Britain (and which I have announced elsewhere). I was at first occupied with Palmifer, but soon discovered that there was a predatory mite feeding upon them. A short inspection satisfied me that it belonged to the genus Cheyletus, and I soon saw that it was not any species that I was acquainted with. Subsequent search (as far as I have been able to carry it) has entirely failed to discover any record of the species, which I therefore presume to be new, although it is quite possible that some one may have observed it whose record I have not found. The state of our knowledge and bibliography as to Cheyletus seems to be as follows: Latreille* first mentioned, named, and described the genus. Koch gives it, and treats of the generic characters and habits; and describes and figures five species in a manner sufficient for identification. He does not in any way deal with the sexes, nor with the larval or pupal states. His species are Ch. eruditus (and casalis, which he regards as a variety); Ch. venustissimus (which I have dealt with below); Ch. hirundinis, and Ch. margi natus. Gervais § gives Eruditus and Marginatus only, and practically simply refers to Koch. DESCRIPTION OF PLATE VI. Cheyletus flabellifer. FIG. 1.-Upper side of female x about 125. FIG. 2.-Under side of female x about 125. a. One of the main tracheal trunks. b. Palpus. c. Lateral mammillary process. d. Anus. FIG. 3.-One of the fan-shaped hairs highly magnified. *Histoire naturelle des Crustaces et des Insectes,' viii. 54. +Enumeratio Insect. Aust.,' 1058, pl. xi. Deutschlands Crustaceen, Arachniden, &c.,' Regensburg, 1839, Heft xxiii. Übersicht die Arachnidensystems, &c.' §Hist. Nat. des Insectes-Apteres,' Walkenaer and Gervais, vol. iii. p. 164. Iconogr. Reg. Anim. Arachnides,' pl. v. f. 8. · Ann. Soc. Ent. Fr.,' 1851. which two or three specimens were found on the ear of a naval officer, near Newfoundland. It appears doubtful whether this is different from Eruditus. The late Andrew Murray says that the armature of the palpi appears to be different, but does not say in what respect; the difference may possibly be due to imperfect drawing or preservation. An account of the mouth, tracheæ, &c., is given by Dujardin.* Kirby and Spence ‡ (on the authority of Schrank, but still it would seem erroneously) state that the larva has eight legs. Mr. Brady § found a specimen in the sea, and called it Robertsoni; it appears, however, to have been Eruditus. Mr. Beck kept and bred Eruditus,|| the name of which he does not give, and treats of the phenomenon of parthenogenesis with regard to it; but he expressly says that he did not find the male, and he does not describe the larva. There is a most exhaustive description of the anatomy and physiology of Eruditus given by Robin and Fumose; they, however, expressly say that they have not found the perfect sexual state, but only the larva and nymph. They say that the perfect state is unknown, and this is repeated by M. Robin in 1877,** but they appear not to have observed Mr. Beck's paper and indeed expressly say that they are not aware that anyone has treated of the subject since Koch. Finally, Andrew Murray, in his 'Economic Entomology,' gives the genus with reference to Koch, Robin, &c., and a drawing which he marks as being the male copied from Robin. It appears to be a copy of Robin's plate xxii., fig. 2; but Robin expressly says he has not found the sexual form, and Murray does not explain why he calls it the male. These are: Generic Characters. 1. The rostrum, large, sharp, and adapted for sucking. 2. The enormous palpi of three joints, armed with falces and pectinated cirri or styles, forming predatory weapons, and being by far the most conspicuous characteristic. 3. The flattened diamond-shaped body with truncated ends. 4. The legs having five joints, the tarsal being terminated by two claws with a double claw between them, and being furnished with a sucker or else fine hairs on the double claw like a brush. *Comptes Rendus,' 1844, xix. 1160. Transactions of Berwickshire Naturalists' Field Club,' vols. ii. and iii. Proc. Zool. Soc.,' 1875. 'Micro. Trans.,' 1866, p. 30. 'Journal de l'anatomie et de la physiologie,' 1867, t. iv. p. 506. 'Traité du Microscope,' 12th ed., Paris, p. 691. |