530 



THE EYE IN EVOLUTION 



Eccles and Sherrington. J . Physiol., 69, 1 



(1930). 

 Eggers. Z. vergl. Physiol, 1, 579 (1924). 

 Ehnbom. Opuscula Entomol., Suppl. VIII, 



Lund (1948). 

 Friedrich. Zool. Jb., Aht. Zool. Physiol., 52, 



637 (1932). 

 Hanstrom. Vergl. Anat. des N erven sy sterns 



der wirbellosen Tiere, Berlin (1928). 

 Proc. not. Acad. Set., 21, 584 (1935). 

 Kungl. Fysiogr. Sallsk. Lund Forhd., 5, 156 



(1935). 

 Heck. Lotos Naturw. Z., Prag., 67/68, 168 



(1920). 

 Herter. Z. vergl. Physiol, 14, 609 (1931). 

 Hess, W. N. J. Morphol, 39, 515 (1924). 

 V. Hoist. Biol. Rev., 10, 234 (1935). 

 Howell. J. exp. Zool, 81, 231 (1939). 

 Janzen. Zool. Jb., Abt. Zool. Physiol, 50, 51 



(1931). 

 Jordan. P fingers Arch. ges. Physiol, 131, 317 



(1910). 

 Z. allg. Physiol, 17, 146 (1918). 

 Just. Z. vergl Physiol, 2, 155 (1924). 

 Kappers, Huber and Crosby. Comparative 



Anat. of the Nervous System oj Vertebrates, 



including Man, N.Y. (1936). 

 Kinoshita. Pflilgers Arch. ges. Physiol, 134, 



501 (1910). 

 Loeb. Pfiugers Arch. ges. Physiol, 56, 247 



(1894). 



McCracken. J. camp. Neurol. Psychol., 17, 



262 (1907). 

 Maxwell. Pfiugers Arch. ges. Physiol., 67, 263 



(1897). 

 Nomura. Tohoku Imp. Univ. Sci. Rep., Sec. 



4, 1, 294 (1926) ; 2, 1 (1927). 

 Prosser. J. camp. Neurol, 59, 61 (1934) ; 62, 



495 (1935). 

 Quart. Rev. Biol, 9, 181 (1934). 

 J. exp. Biol, 12, 95 (1935). 

 Physiol. Rev., 26, 337 (1946). 

 Comparative Aniinal Physiology, London 



(1950). 

 Rietschel. Zool. Anz., Ill, 109 (1935). 

 Roeder. Biol. Bull, 69, 203 (1935). 



J. exp. Zool, 76, 353 (1937). 

 Sanders and Young. J. Neurophysiol, 3, 501 



(1940). 

 Smallwood and Holmes. J. conip. Neurol, 43, 



327 (1927). 

 Snodgrass. Smithsonian Misc. Coll., 11, No. 8 



(1926). 

 Stough. J. comp. Neurol, 40, 409 (1926) ; 



50, 217 (1930). 

 Swartz. J. comp. Psychol, 9, 17 (1929). 

 V. Uexkull. Z. Biol, 31, 584 (1895), 



Ergebn. Physiol, 3, 1 (1904). 

 Welsh. J. exp. Zool, 86, 35 (1941). 

 Wigglesworth. The Principles of Insect 



Physiology, London (1953). 

 Young. Proc. XIX int. physiol Congr., 



Montreal, p. 99 (1953). 



THE CENTRAL NERVOUS SYSTEM 



A central nervous system is characteristic of the Chordates which possess 

 a brain and dorsal nerve-cord replacing the cerebral ganglion and the 

 ventral cord of the Invertebrates, the whole being initially supported by a 

 notochord and eventually encased in a protective bony skull and vertebral 

 colunui. In the Proto- chordates, however, the nervous system is exceed- 

 ingly primitive. 



We have already seen ^ that in the hemichordates {Balanoglossus) the nervous 

 system is essentially a peripheral nerve-net centred round a dorsal nerve-cord arising 

 as a longitudinal groove of ectoderm connected by a band around the collar of the 

 animal with a ventral nerve. There is as yet no evidence of a brain. In larval 

 TUNicATES there is a poorly developed ganglionic brain connected with the median eye 

 and continued in a dorsal nerve-cord - ; but in the sessile advxlt Ascidian the nervous 

 system recedes until it is represented merely by a single ganglionic mass from which 

 a few short nerve -filaments ennerge.^ In the acrania, the brain of Arnphioxus 

 {Branchiostoma) is almost undeveloped and is represented by a small cerebral vesicle, 

 but the dorsal cord with its central canal is well formed and sends off two anterior 

 cerebral nerves and a pair of segmental nerves, dorsal and ventral, to each myotome 

 (Fig. 236). 



Among VERTEBRATES the central nervous system attains a structural 

 compl( ^-'ty and functional coordination unparalleled in the animal kingdom, 

 1 p. 227. 2 p. 228. 3 p_ 228. 



