Febbuaky 28, 1908] 



SCIENCE 



341 



have been secured from various localities 

 in this country and in South America. 



The Development of the Ascocarp of 

 Melanospora: Professor J. B. Overton, 

 University of Wisconsin. (By title.) 



Progressive Cleavage in Didymium: Pro- 

 fessor R. A. Haepee, University of "Wis- 

 consin. (By title.) 



On the Development of Immunity for 

 Heart-rot Diseases in Trees: Dr. Her- 

 mann VON ScHEENCK, Missouri Botan- 

 ical Garden. (By title.) 



The Influence of the Swaying of the Wind 

 on the Formation of Mechanical Tissue 

 in Plants: Professor F. C. Newcombe, 

 University of Michigan. (By title.) 



A Study of Edaphic Conditions in Peat 

 Bogs near Ann Arior: Dr. G. P. Burns, 

 University of Michigan. (By title.) 

 Duncan S. Johnson, 



Secretary 

 Johns Hopkiks Univeksity 



SCIENTIFIC BOOKS 

 Evolution of Mammalian Molar Teeth to and 



from the Triangular Type. By Henry 



Paiefield Osboen, Sc.D., LL.D., D.Sc. 



Edited by W. K Gregory, M.A. Pp. 250. 



New York, The Macmillan Company. 1907. 



This book, the most valuable contribution 

 to mammalian odontology since that of Sir 

 Richard Owen, consists of a series of col- 

 lected and revised researches upon tritubereuly 

 with new sections on the forms and homol- 

 ogies of the molar teeth in the different 

 orders of mammals. The theory of tri- 

 tubereuly was a conception of the late Pro- 

 fessor Cope, but was elaborated by Professor 

 Osborn, who has been by far the greatest ex- 

 ponent of the idea. Four principles have been 

 developed in connection with the general 

 theory: (1) That in the most primitive Ter- 

 tiary mammalia there are " three main tuber- 

 cles on the crowns of hoth upper and lower 

 molars, disposed in triangles " ; primitive tri- 

 tubereuly. (2) Origin of the tritubercular 



types from the single reptilian cone. " The 

 tritubercular type sprang from a single conical 

 type by the addition of lateral denticles." 

 (3) Cusp addition or differentiation; "a 

 process analogous to budding or outgrowth in^ 

 other tissues." An opposing theory to this 

 is that of concrescence. (4) Reversed upper 

 and lower triangles. "In the lower molars- 

 the reptilian cone is external and the two 

 denticles internal, while in the upper molars 

 the reverse is the case, namely, the reptilian 

 cone is internal and the denticles are external."' 

 It is on this principle that the Osbornian.' 

 nomenclature, implying a serial homology be- 

 tween the cusps of the upper and lower 

 molars, is based. As applied to the lower 

 molars this principle is generally accepted; 

 but as applied to the upper teeth, it has been 

 most vigorously opposed in the light of three 

 different classes of positive evidence — embry- 

 ological, anatomical and paleontological. The 

 embryological evidences seem to point to the 

 antero-external cone (Osborn's paracone) as 

 of the greatest antiquity and therefore the 

 reptilian cone. This is also borne out by the 

 analogy of the premolar cusp development 

 (premolar-analogy), and by that of the lower 

 molars. Evidence in favor of Osborn's theory 

 is derived from paleontology, and is also 

 shown by the mechanical development of the 

 cusps, while on the other hand recent interpre- 

 tation by Gidley of paleontological evidence 

 is in harmony with that of embryology and 

 with the premolar analogy theory. 



In the summary of his introduction Pro- 

 fessor Osborn says : " That the four great^ 

 principles of molar evolution do not stand or 

 fall together." The first principle, that of 

 primitive tritubereuly, is now almost un- 

 deniable; the reptilian cone origin theory next' 

 in order of demonstration and acceptance ; the 

 cusp addition theory finding at present more 

 advocates than the opposing idea of con- 

 crescence. Finally the greatest conflict of 

 evidence occurs with reference to the homol- 

 ogies of the upper and lower cusps. There 

 is no middle ground; either the Cope-Osboru 

 theory is correct and the premolar-analogy - 

 plus the embryological theory wrong, or the- 

 reverse is true. 



