THE WONDER OF LIFE 609 



of the pelvic vestiges of the Finner (Balcenoptera physalus), 

 the Blue Whale (B. sibbaldi), Rudolphi's Rorqual (B. 

 borealis) and the Humpback (Megaptera boops) show 

 that the bones, like many vestigial structures, are in a state 

 of considerable variability. 



We have given two figures of a very interesting and 

 puzzling structure connected with the roof of the brain 

 in Vertebrates. From the region known as the 'tween-brain 

 or optic thalami there is a dorsal up-growth, usually con- 



FIG. 94. Vertical section showing the pineal eye of the adult slow- 

 worm, Anguis fragilis. (After Hanitsch.) 1 , Cuticle ; 2, Epidermis ; 

 3, Connective tissue ; 4, Parietal bone of the skull ; [5, Lens of pineal 

 eye ; 6, Wall of pineal eye ; 7, Epiphysis or upgrowth from the 

 brain. It is here continuous with the stalk of the pineal eye. 

 According to Hanitsch, the pineal eye in the slowiworm is 

 sensitive to changes of temperature. 



sisting of two parts, a pineal organ or epiphysis proper, 

 and a parietal organ, which generally springs from the 

 epiphysis, but may have an independent origin in front of 

 it. Perhaps they were originally the right and left mem- 

 bers of a pair. The parietal organ is often atrophied, 

 but in some cases, especially in Reptiles, it is terminally 

 differentiated into a little ' pineal body.' In the New 

 Zealand ' lizard ' (Sphenodon) and in the slow- worm 

 (Anguis) it shows distinct traces of eye-like structure. 



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