t'.l PHYSIOLOGICAL SERIES. 



anterior pointed region terminates in a median eye-spot 

 and give- off two pair- of purely sensory nerves to the 

 Miout. From tlie rot of the cord a scries of mixed and 

 motor ner\e- ari-e. iliat correspond in number and position 

 to the >epta -between tlie myotomes and consequently 

 alternate on either side. The central canal is lined by a sup- 

 porting epithelium. This is surrounded, as in Vertebrates 

 by a layer of ganglion-cells, \vhile the outer parts of the 

 cord consist of aon-medullated nerve-fibres of different 

 sizes. Some f these, -,\ Inch arise from giant ganglion-cells 

 that lie across the canal in the anterior and posterior thirds 

 of the cord, are of remarkably large sixe and remind one of 

 Mitller'- fibres in < 'ydostomes or of the giant fibres in 

 Invertebrates In front the canal broadens out to form a 

 cerebral vehicle, that probably corresponds with the three 

 primary vesicles of tlie vertebrate brain. A small evagina- 

 tionof it<dor-o-anterior wall extends towards the olfactory 

 jit and indicates the last closed connection of the central 

 canal with the exterior (a similar excrescence occurs in the 

 embryos of Vertebrates) ; while below, another median 

 _ination apparently represent- the infundibulum. As 

 the walls of this " brain" region are thinner than in other 

 parts of the cord, there is no external sign of a cerebral 

 enlargement. 0. C. A. 1^47. 



\Villey. Amphioxus/ 1894, p. 82. 



VERTEBRATA. 



BRAIN. 



Kdinger, Anat. Central Nervous System, 5th ed. (Kngl. 



trail-.) IH'.i'J. 

 Kdinger. Ahhandl. Sem-kcnberg. Gesell., Bd. xv. 1890 



(Cmhntm). 



Haller. Morph. .lahrb.. T.d. \\\i. l.sjis. j,. (i;',^ (/y/7,//,^/.). 



CYCLOSTOMI. 



D. 67. The brain of a Sea Lamprey (/V//v./// t yron marinus). 



Tlie Cy -lo-tomes have an extremely simple brain, 



