EVOLUTION OF THE PARIETAL ORGAN 



479 



CLASSES OF ANIMALS E- OIFFERENT 

 SEQUENCE OF GEOLOGICAL PERIODS b ESTIMATED NUMBER OF YEARS TYPES OF EYE 



iRY, PLEISTOCENE 6 PLEIOCENE 



TERTIARYqliGOCENE & EOCENE — 



GREAT MAMMALS 



SECONDARY or MEZOZOIC 



$5,000,000 TO 240,000,000 



JURASSIC 



155. OOO.OOO TO 195,000.000 



TRIASSIC 



190,000,000 TO 240,000,000 



PE RM I AM 



PRIMARY 



or 



PALEOZOIC 



2/5,000,000 TO 700000 000 



215. OOO, OOO TO 280, OOO, OOO 



CARBONIFEROUS 



2 SO OOO.OOO To 33U.OOOOOO 



370, 000,000 



DEVONIAN 



360. OOO, OOO TO 420 OOO. OOO 



SILURIAN 



3 90.000 OOO TO 46OOOOO00 



ORDOVICI AN 



480,000,000 TO 590 OOO.OOO 



CAMBRIAN 



550,000 OOO TO 700,000,000 



ARCHAEAN 



MAMMALS 



BIRDS 



GREAT REPTILES 



LARGE PARIETAL FORAMEN 

 or IMPRESSION IN SOME 

 REPTILES & AMPHIBIANS, 

 MAMMAL-LIKE REPTILES 

 LAST TRILOBITES 



GREAT AMPHIBIA 



LAND SCORPIONS 



STEGOCEPHALIA 

 MAILED FISHES 



MARINE SCORPIONS 



EXISTENCE OF PAIREO-EYES OF 

 VERTEBRATES PRESUMED 



FIRST FISHES & INSECTS 



VERTEBRATES APPEAR 



INDICATIONS OF 

 MEO'AIN &-LATERAL PAIRED-EYES 

 OF INVERTEBRATES 



FIRST TRILOBITES 



EXISTENCE OF PAIRED-EYES PRESUMEO 

 (WORMS. CRUSTACEANS. MOLLUSCS) 



EVOLUTION OF PHOTO-RECEPTIVE ORGANS 



INVERTEBRATES 



Fig. 324 t — Geological Chart indicating the Order in which Organs Sensitive 

 to Light and various Types of Eye have been evolved, and also the 

 Estimated Age in which the Different Classes of Animals have been 

 found. (Modified from Scheme and Data published by Gaskell and 



