492 THE POPULAR SCIENCE MONTHLY. 



WHAT AMERICAIN ZOOLOGISTS HAVE DONE FOR 



EYOLUTION.* 



By Trofessor EDWAED S. MOKSE. 

 \_Concluded.'\ 



TO those who have already been startled by the memoir of Dr. W. 

 Baldwin Spencer on the presence and structure of the pineal gland 

 in Lacertilia, and the evidence that it represents a third eye in a rudi- 

 mentary condition, it will be interesting to know that among some of 

 the earlier mammals the pineal gland may have assumed functional 

 importance as an eye. Professor Henry F. Osborn f shows that in the 

 skull of the curious mammal Tritylodon, of Owen, there is seen a 

 parietal foramen in exactly the same position and relation as in the 

 lizard Sphenodon. 



Professor Osborn regards this fact of remarkable interest, as it 

 adds greatly to the rapidly accumulating evidence for the reptilian 

 affinities of the mammalia. Professor Owen, in the description of 

 this unaccountable opening, suggested that it might be due to posthu- 

 mous injury. 



Professor Marsh, J in a description of the skull of Diplodocus, a 

 Dinosaur, describes a fontanelle in the parietal on the median line 

 directly over the cerebral cavity. He adds, however, that this may be 

 merely an individual variation. 



Professor Cope *^ observes an enormous fronto-parietal foramen in 

 the skull of E)npedocles tnolaris, a curious creature from the Permian. 



It would appear evident from these facts that at one time the 

 pineal gland, which in the mammals is in a rudimentary condition, 

 and in certain Lacertilia sufficiently perfect, as an eye, to be sensitive 

 to light impressions at least, was, in certain extinct mammals and 

 reptiles, of large size and functionally active. It is a significant fact 

 that no sooner does some one opposed to evolution undertake to lay 

 down the law by setting a boundary to type-features, than a dis- 

 covery is made that breaks down the barrier. Thus, Dr. Thomas 

 Dwight, II in an interesting memoir on the "Significance of Bone 

 Structure," in which he makes a brave defense for teleology, says, in 

 speaking of the persistence of the vertebrate plan, " There are never, 

 for instance, more than two eyes or one mouth or two pairs of limbs," 

 and, lo ! an extra eye is immediately added. 



* Address of the retiring President of the American Assoeiation for the Advancement 

 of Science, delivered at the New Yorlt meeting, August 10, 18S7. 



f " Science," vol. ix, p. 114. 



X "American Journal of Science and Arts," vol. xxvii, p. 161. 



* "Proceedings of the American Philosophical Society," 1S7S, p. 516. 

 J " Memoirs of the British Society of Natural Ilistorj," vol. iv, No. 1. 



I 



