470 



DE. H. Vf. MAEETT TIMS ON" THE 



evolution is, to a certain extent " (the italics are mine), "repeated 

 in embryonic development." However, we can gather from this 

 that Osborn admits the validity of the assumption. 



Upon this basis, let us see how the facts may be reconciled with 

 the tritubercular theory. According to this, the Protoeone should 

 be developed first, and the Paracone and Metacone almost simul- 

 taneously but at a later period, and the talon, or heel, still later. 

 This is the order in which the various cusps have arisen, according 

 to Prof. Cope (2) ; consequently this is the order in which they 

 should appear ontogenetically. 



The cusp-development has been worked out by Eose (22) in the 

 Primates and Marsupials, and by Taeker (25) in the Ungulates. 

 Their results are seen in the accompanying Table (II.), copied 







Table II. 











"Upper Molars. 



. 





1. 



2. 

 3. 

 4. 



Primates. 

 Paracone. 

 Protoeone. 

 Metacone. 

 Hypocone. 



Marsupials. 

 Paracone. 

 Protoeone. 

 Metacone. 

 Hypocone. 



Lower Molars. 



Ungulates. 



Paracone. 



Metacone. 



Protoeone. 



Hypocone. 



1. 



2. 

 3. 

 4. 



1. 

 2. 

 3. 

 4. 

 5. 



Protoconid. 



Metaconid. 



Hypoconid. 



Entoconid. 



Hypoconulid. 



Protoconid. 

 Paraconid. 

 Hypoconid. 

 Entoconid. 

 Metaconid. 



Protoconid. 

 Metaconid. 

 Hypoconid. 

 Entoconid. 



1. 

 2. 

 3. 

 4. 



from a paper by Osborn (13), and with them my own results, 

 as seen in' the Dog, are in agreement. From a study of this 

 table the most striking fact is revealed that while in not one of 

 the four orders does the Protoeone develop first, the Protoconid 

 does so in every instance. This is a very important point. 



In the above-mentioned address by Osborn (15), the fact 

 of the agreement in the lower jaw and disagreement in the 

 upper jaw is thus referred to ; he says : — " In the lower molar 

 teeth the order of calcification is precisely the order of evolution;" 

 and after dealing with this order of development, he goes on 

 to say : " So we find that the order of embryonic development 

 exactly repeats the order of historical development, and in every 

 way presents the strongest kind of confirmation of the theory of 

 cusp-formation which we have been discussing." He omits to 

 mention that the Paraconid does not develop at all. 



