VERTEBEATES FROM A CRUSTACEAN-LIKE ANCESTOR. 441 



20. Beard. — " The Parietal Eye of the Cyclostome Fishes," ' Quart. Journ. 



Micr. Sci.,' 1888. 



21. Lankester & Bourne. — " The Minute Structure of the Lateral and 



Central Eyes of Scorpio and Limulus," this Journal, vol. xxiii, p. 177. 



22. Grenacheb. — ' Sehorgan der Arthropodeu,' Goltingen, 1879. 



23. Spencer. — "On the Presence and Structure of the Pineal Eye in Lacer- 



tilia," this Journal, 1886. 



24. De Graaf. — ' Bouw en de Ontwikkeling der Epiphyse bij Amphibien 



en Eepiilien,' Leiden, 1886. 



25. Patten. — "Studies on the Eyes of Arthropods," 'Journ. of JMorphol.,* 



vol. i, p. 193. 



26. Patten. — " Studies on the Eyes of Arthropods," 'Journ. of Alorphol.,' 



vol. ii, p. 97. 



27. Bellonci. — " Sur la structure et les rapports des Lobes Olfactifs dans les 



Arthropods superieurs et les Vertebres," ' Archives Ital. de Biologic,' 

 vol. iii, p. 191. 



Cambridge; March, 1890. 



EXPLANATION OF PLATES XXV, XXVI, XXVII, 



XXVIII, 



Illustrating Mr. W. H. Gaskell's paper " Ou the Origin of 

 A^ertebrates from a Crustacean-like Ancestor." 



Examination of Reference Letters. 



b. V. Blood-vessel, b. s. Blood-sinus, cb. Cerebellum, cer. Cerebral and 

 olfactory lobes (supra-oesophageal ganglia), ch^, ch„, ch^. Choroid plexuses 

 (free walls of cephalic stomach). corn. ten. Commissura tenuissima. cr. 

 Cranial wall. ff. h. r. Right ganglion habenulse (right optic ganglion), g. h. I. 

 Left ganglion habenulse (left optic ganglion). I. Arachnoidal tissue (cephalic 

 liver). I. e. Lens of pineal eye. /. d. Ganglion iuterpedunculare (duct of 

 cephalic liver). /. i. Lobus infundibuli (old oesophagus). /. t. Lamina 

 termiualis (anterior end of cephalic stomach). M. b. r. Eight Meynert's 

 bundle. M. b. I. Left Meynert's bundle, med. Medulla of pineal eye. M.f. 

 Miillerian fibres, n. Nerve of pineal eye. nc. Notochord. n. g. Nerve- 

 cells of grey matter, o. c. Central cavity of optic vesicle. oJ. Olfactory 



