478 THE PINEAL ORGAN 



sense-organ of vertebrates, and designated the median eyes of inverte- 

 brates as such, or as frontal, triplacodal, or entomostracan eyes. We do 

 not, however, wish it to be inferred that we consider the parietal sense- 

 organ of vertebrates has arisen quite independently of the median eyes 



EPIPHYSIS SHOWS EVIDENCE OF DEGENERATION 

 IN ADULT ANIMALS. PARIETAL EYE ABSENT 



PARIETAL EYE WELL DEVELOPED 



P NERVE ENDS IN R HABR GANGLION 



IN L.VIVIR, PINEAL SAC LARGE 



PARIETAL EYE WELL DEVELOPED P NERVE 



ENDS IN L. HABR GANGLION: WALL OF 



PINEAL SAC HIGHLY DIFFERENTIATED 



PARIETAL FORAMEN LARGE 

 LARGE ORBITAL CAVITIES 



Parietal foramen well 

 developed. paired lateral 

 orbital cavities. 



EPIPHYSIS PRESENT 



PARfETAL EYE ABSENT. TUBULAR 

 EPIPHYSIS WITH EXPANDED 

 TERMINAL VESICLE 



PARIETAL EYES WELL 

 DEVELOPED. PAIRED 

 LATERAL EYES WITH 

 INVERTED RETINA AND 

 ECTODERMAL LENS 



TORNARIA LARVAE ..HEMICHORDA 

 WITH EYE-SPOTS/ UROCHORDA 

 ON APICAL PLATE CEPHALOCHORDA J J 



PAIRED MEDIAN EYES AND PAIRED LATERAL EYES 

 ARE SOMETIMES PRESENT, OF UPRIGHT TYPE 



EXTINCT BRANCHES OF 

 NO TRACES ARE LEFT 



EPIPHYSIS WELL DEVELOPED IN YOUNG 

 BIRDS FOLLICULAR EPITHELIUM DEGENERATES 

 IN OLDER BIRDS AND THE CAVITIES OF THE 

 FOLLICLES TEND TO BECOME OBLITERATED 

 PARIETAL EYE ABSENT 



STALKED. LATERAL EYES, OF COMPOUND 

 AND HIGHLY DIFFERENTIATED, UPRIGHT 

 TYPE! ENTOMOSTRACAN OR TRIPLACODAL 

 M OF MEDIAN EYE 



CYCLOSTOM 



MEDIAN PAIRED EYES AND LATERAL 

 PAIRED EYES LENS SINGLE 

 RETINA UPRIGHT OR INVERTED 



AN FRONTAL OCELLI AND 

 RAL FACETED EYES OF 

 ILE TYPE 



simple uprighteyes 



types of simple upright eyes, 

 lateral; dorsal; on edge of 

 mantle, having ectodermal 

 cellular lens & inverted 

 retina. highly differentiated 

 eyes in cephalopods. 



TROCHOPHORE LARVAE WITH EYESPOTS ON APICAL PLATE 



SIMPLE OCELLI OR PIGMENT SPOTS, 



OF UNICELLULAR OR MULTICELLULAR TYPES. 



Fig. 323. — Scheme indicating the General Distribution of Different 

 Types of Median and Lateral Eyes in the Animal Kingdom. 



of invertebrates. Further, we have used the term " parietal eye " in the 

 singular although, as explained elsewhere, it may represent in some cases 

 one member of a pair of median eyes or in other cases be formed by the 

 fusion of the right and left members of a pair of primarily bilateral 

 organs. 



