274 
Transactions of the Society . 
VII . — On the Form and Proportions of the Brain in the Orihatidse 
and in some other Acarina. 
By A. D. Michael, President R.M.S, F.L.S., &c. 
With a Note by E. M. Nelson, F.R.M.S. 
{Read 17 th April , 1895.) 
Plate VI. 
When, some twelve years ago, I read a paper before this Society on 
the Anatomy of the Oribatidm * there was one portion of the internal 
anatomy which was scarcely dealt with at all, namely, the brain and 
nervous system. That paper, however, together with the chapters 
on anatomy in my subsequently published ‘ British Oribatidae,’ f still 
practically contains all that is known respecting the internal anatomy 
of these creatures. At that time section-cutting had not attained the 
EXPLANATION OF PLATE VI. 
A, supra-cesophageal ganglion of the brain. B, sub-oesophageal ganglion of 
the brain. C, compressor muscles of pharynx cut across, cl, cortical layer of 
brain, cm, constrictor muscles of oesophagus. D, distensor muscles of pharynx. 
F, fibrous layer of brain. M, maxillary lip. N, neurilemma. Nph, pharyngeal 
nerve, nu, nuclei, ph, pharynx, ce, oesophagus, rph, roof of pharynx, t, tracheae. 
V, ventriculus (lumen of). W, wall of ventriculus. 
i All the figures are of adult specimens, and all the sections are drawn from 
specimens hardened with picro-sulphuric acid or Flemming’s fluid, and stained w ith 
haematoxylin or picro-carmine. 
Fig. 1. — Brain of Leiosoma pcilmacinctum (Oribatidae), x 240. Sagittal median 
section, showing the very wide oesophagus passing through the brain and! 
dividing it (in this section) into two halves. 
„ 2. — The same species ; sagittal section of brain not median, but taken at the 
side of the oesophagus, X 240 ; showing the fusion of the supra- 
cesophageal and the sub-oesophageal ganglia into one mass. 
„ 3. — Brain of Ctplieus latus (Oribatidae), x 175. Sagittal median section. 
„ 4. — Brain of same species, transverse section about the centre of the brain, 
X 175. 
„ 5. — Brain of Gamasus terribilis $ . Sagittal median section, x 120. 
„ 6. — Brain of Sejus togatus (Gamasidae), x 175. Sagittal median section. 
„ 7. — Brain of Trombidium (sp.) probably holosericeum, X 175. Sagittal median 
section. 
„ 8. — Brain of Trombidium fuliginosum Herm., seen from above, x 110. 
„ 9. — Brain of Tetranychus lintearius (Dufour), x 300. Sagittal median section. 
„ 10. — Brain of Thycis petrophilus (Hydrachnidae), x 120. Sagittal median 
section. 
„ 11. — Brain of Cheyletus fiabellifcr, x 250. Sagittal median section. 
„ 12. — Brain of Glyciphagus platygaster $ (Tyroglyphidae), x 175. Sagittal 
median section. 
„ 13.— Brain of the same species and sex, x 175. Transverse section about the 
centre. 
„ 14. — Brain of the same species $ , x 175. Transverse section about the centre. 
f London (Ray Society), 1884, 1888. 
* This Journal, 1883, pp. 1-25. 
