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 hoops) show 

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

 of considerable variabiUty. 



We have given two figures of a very interesting and 

 puzzUng 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 f ragilis. (Aper 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 slow-worm 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 httle '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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