784 TBE POPULAR SCIENCE MONTHLY. 



tlie pineal gland is not covered. It lies just beneath the parietal 

 suture, that portion of the top of the skull where the bones are 

 still ununited in new-born children. In many reptiles, notably 

 Hatteria (Fig. 1) and Aurelia, the pineal gland is found to be an 

 optic lobe, united to the nerve-stalk of a true eye, richly supplied 

 with a branched blood-vessel and nerve. Although this eye still 

 possesses every essential part of a visual organ, yet degenerative 

 changes have set in, which show that it has been long useless. In 

 Varanus giganteus (Fig. 2), where a scale on the top of the head is 

 fitted by its transparency and whiteness to act as a cornea, a large 

 mass of pigment has accumulated just beneath, effectually prevent- 

 ing the possibility of any rays of light reaching the retina. In 

 Hatteria, the eye appears fitted in all respects for vision, but a thick 

 band of connective tissue has formed above it, and there is no 

 modified scale. In both animals, Hatteria and Varanus, the rods 

 and cones of the retina are strangely elongated in certain parts, as 

 though from straining to catch the last rays of vanishing light. 

 The rods of this portion are at least three times the length of the 

 ordinary ones, and are in connection with a special group of nu- 

 cleated cells. 



In modern amphibians the greatly degenerated eye is separated 

 entirely from the pineal stalk, though a connection still exists 

 during embryonic life. But there is reason to think that among 

 ancient amphibians — more especially among the labyrinthodonts 

 — the pineal eye reached its very highest development, since it is 

 found outside the skull. A large parietal opening, with rough- 

 nesses of the skull-bones serving as attachments for j)owerful 

 muscles, is found in the great extinct amphibians and reptiles. 

 The pineal eye was pre-eminently a sense-organ of pre-tertiary 

 periods ; it has probably never been functional since these remote 

 ages, and yet its rudiments persist in every human brain. More- 

 over, these eyes are of the invertebrate type, pointing back to that 

 conjectural molluscoid ancestor which was " transparent and had 

 a median eye." 



The records of pathology teem with instances of rudimentary 

 organs which have lost their use and have become sources of 

 danger and disease. I venture to think these facts are far too 

 little known to those outside of the medical profession who are 

 interested in evolution. It is not necessary to do more than allude 

 to the " appendix vermiformis," since every reader of the " Descent 

 of Man " will remember it as the typical instance of a mischievous 

 rudimentary organ, given by Darwin. 



All mammals possess, during their embryonic life, three sets of 

 kidneys. The first set of tubules cease very early in fetal life to act 

 as kidneys ; they take on a new function of supreme importance, 

 their ducts becoming the oviducts in most fishes, amphibians, rep- 



