72 
J. BEARD. 
14. Spencer, W. B. — “ On the Presence and Structure of the Pineal Eye in 
Lacertilia,” ‘Quart. Journ. Micr. Sci.,’ Oct., 1886, vol. xxvii, part 2, 
p. 239. 
15. Rabl-Ruckhard. — “Zur Deutuug u. Entwickelung des Gehirus der 
Kuochenfische,” ‘ Arcliiv f. Anat. u. Physiol.,’ 1882, p. 111. 
16. Wiedersheim, R. — “ Das Gehirn von Ammocoetes u. Petromyzon 
Planeri,” ‘ Morphol. Studien,’ I. 
17. Wiedersueim, R. — “ Ueber das Parietal Auge der Saurier,” ‘ Anat. 
Anz.,’ Jahrgaug I, No. 6, 1886, p. 148. 
DESCRIPTION OF PLATES VI & VII, 
Illustrating Dr. Beard’s Memoir on “ The Parietal Eye of the 
Cyclostome Fishes.” 
Alphabetical List of Reference Letters. 
ant. Anterior, bl. Blood, br. Brain, cn. Cones of retina, co. Coagu- 
lated fluid, c. t. Connective tissue, ep. Epidermis, gl. trb. Ganglion tra- 
beculoe. 1. Lens cells, md. br. Mid-brain. n l . Inner nuclear layer, m 2 . 
Outer nuclear layer. n~. gl. Ganglion of outer layer. P. E. Parietal eye. 
p. s. and p. Black pigment. r. Retina. rd. Rod elements of retina. 
s.f Skull fossa for parietal eye. sic. Skull, s. Stalk, th. Thalamence- 
phalon. 
All the figures in Plates VI and VII are from camera lucida drawings, 
except A, B, and C. 
PLATE VI. 
Eig. 1. — Longitudinal section through skull of adult Petromyzon 
planeri, showing parietal eye ( P . E.) in situ. Zeiss C, oc. 2. 
Eig. 2. — Transverse section of ordinary eye of Ammocoetes, drawn under 
the same magnification as the following figure. 
Fig. 3. — Transverse section of parietal eye, taken from the same animal 
as preceding figure for comparison with it. Figs. 2 and 3 under same magni- 
fication, viz. Z. D, oc. 2. These two figures are from one of Herr Schwarz’s 
preparations. 
Fig. 4. — Parietal eye of adult Petromyzon planeri in longitudinal 
section. The only traces of black pigment are present at ps. Zeiss F, oc. 2. 
