130 



BULLETIN : MUSEUM OF COMPAllATIVE ZOOLOaY. 



PAGE 



I). Summary for selachians . 178 



III 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 190 



3. Polypterus 190 



4. Acipenser 191 



B. Critical discussion . . . 192 



C. Summary for ganoids . 194 

 IV. Teleosts 195 



A. Historical 195 



B. Morpliology of the mesen- 



cephalon 196 



1. The median zone . 196 



2. The torus longitudinalis 197 



C. The optic reflex apparatus 199 



1. Siluridae 199 



2. Cyprinidae 200 



3. Salmonidae 201 



4. Poeciliidae 205 



5. Amblyopsidae .... 205 



6. Esocidae 207 



7. Gasterosteidae . . . 207 



8. Atherinidae 207 



9. Pomatomidae .... 208 



10. Stromateidac .... 209 



11. Serranidae 209 



12. Sparidae 210 



13. Sciaenidae 210 



14. Labridae 212 



15. Balistidae 215 



16. Monacanthidae . . . 215 



17. Cottidae 215 



18. Cyclopteridae .... 215 



PAGE 



19. Triglidae 215 



20. Malacanthidae . ... 215 



21. Batrachoididae ... 216 



22. Gadidae 21G 



23. Pleuronectidae . . . 21C 



24. Lophiidae 217 



I). Critical discussion . . . 217 



E. Summary for teleosts . . 221 



IL Phj'siological 222 



A. Comparative physiology . . 222 



1. The ' Flight Keflex ' . . . 222 



2. llelation of the state of the 



apparatus to activity . . 224 



3. Effect of degeneration of the 



eye on the apparatus . . 225 



4. Relation between the optic 



lobes and the optic reflex 



apparatus 226 



5. Relative importance of the 



visual sense 220 



B. Experimental physiology . 227 



1. Material 228 



2. Method of operation . . . 228 



3. Experiments 229 



C. Ph^^siological value of the 



apparatus 231 



1. Rate of transmission of the 



nervous impulse .... 231 



2. Time relations of central 



processes 233 



3. Delay in the conduction patii 235 



a. Central delay 23G 



h. Delay in transmission 



through the cell body . 238 



4. Time of optic reflex reaction 239 



5. Time saved by the optic re- 



flex apparatus 239 



Bibliography 241 



Explanation of plates 257 



