130 



BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



PAGE 



D. Summary for selachians . 178 



m. Ganoids 179 



A. Observations 179 



1. Amia 179 



a. Development . . . 179 

 (1.) Optic reflex cells 181 

 (2.) Posterior canal- 

 cells .... 185 



b. Adult 188 



2. Lepidosteus lUO 



3. P()lyi)terus 190 



4. Acii)enser 191 



B. Critical discussion . . . 192 



C. Summary for ganoids . 194 

 IV. Teleosts 195 



A. Historical 195 



B. Morphology of the mesen- 



cephalon 190 



1. The median zone . . . 19G 



2. The torus loiigitudinalis 197 



C. The optic reflex apparatus Vj9 



1. Siluridae 199 



2. Cyprinidae 200 



3. Salmonidae 201 



4. Poeciliidae 205 



5. Amblyopsidae .... 205 



6. Esocidae 207 



7. Gastcrosteidae . . . 207 



8. Atherinidac 207 



9. Pomatomidae .... 208 



10. Stromateidac .... 209 



11. Serranidae 209 



12. Sparidae 210 



13. Sciaenidae 210 



14. Labridae 212 



15. Balistidae 215 



IG. Monacanthidae . . . 215 



17. Cottidae 215 



18. Cyclopteridae .... 215 



PAGE 



19. Triglidae 215 



20. Malacanthidae. . . . 215 



21. Batrachoididae . . . 21G 



22. Gadidae 210 



23. Pleuronectidae ... 210 



24. Lophiidae 217 



T>. Critical discussion . . . 217 



E. Summary for teleosts . . 221 



II. Physiological 222 



A. Comparative jjh^'siology . . 222 



1. The ' Fhght Keflex "... 222 



2. Kelation of the .state of the 



apparatus to activity . . 224 



3. Effect of degeneration of the 



eye on the apparatus . . 225 



4. Kelation between the optic 



lobes and the optic reflex 



apparatus 226 



5. Kelativc importance of the 



visual sense 22G 



/). Experimental physiology . . 227 



1. Material 228 



2. Method of operation ... 228 



3. Experiments 229 



C. Physiological value of the 



apparatus 2;>l 



1. Kate of transmission of the 



nervous impulse .... 231 



2. Time relations of central 



processes 233 



3. Delay in the conduction path 235 



a. Central delay 2.">G 



I). Delay in transmission 



through the cell body . 238 



4. Time of optic reflex reaction 239 



5. Time saved by the optic re- 



flex api)aratus 239 



Bibliography 241 



Explanation of plates 257 



