Mav 31, 



1894] 



NA TURE 



lOI 



including 107 figures, roughly drawn, but characteristic. 

 They show most of the common and seemingly capri- 

 cious forms assumed by stalagmitic deposits. Certain of 

 the observations are somewhat trivial, such as the refer- 

 ence to the ■' profile of Gladstone " in the centre of one 

 stalactite, and the comparison with the ''hind-quarters 

 of an elephant" in another. The author has not availed 

 himself of the assistance which would have been obtained 

 by examining thin sections of the deposits under the 

 microscope. 



Botanical Charts ami Definitions. By Miss A. E. 

 Brooke and Miss A. C. Brooke. (London : G. Philip 

 and Son, 1894.) 

 It is notorious that examinations in elementary 

 practical chemistry are frequently little more than tests 

 of capacity for remembering analytical tables. This 

 little book will serve the same purpose in botany that 

 tables of analysis do in chemistry. In thirty-four pages 

 the authors summarise the work required for the South 

 Kensington (Elementary) and the Oxford and Cam- 

 bridge Junior Local Examinations in Botany. Chartsand 

 definitions are given of sub-kingdoms, classes, orders, and 

 doral whorls ; of root, stem, leaf, inflorescence, and fruit. 

 These, with definitions of terms of cohesion and ad- 

 hesion, enable the student to classify a plant on the lines 

 of the table of analysis wiih which the book concludes. 

 We are afraid that the compilation will induce cramming 

 for the examinations for which it is intended ; but if this 

 be avoided, and the charts are only used as supple- 

 mentary to oral teaching and demonstration, they will 

 help students to acquire a clear view of the relation and 

 arrangement of the parts of a plant. 



TIic Great Glotte : First Lessons in Geography. By A. 



Seeley. (London: Seeley and Co., 1894.) 

 A SIMPLY worded and instructive primer of geography, 

 printed in clear type, and illustrated with numerous cuts and 

 diagrams. The book does not merely consist of lists of 

 lengths of rivers, heights of mountains, populations 

 of cities, and similar statistics, but is a compendium 

 of facts calculated to interest the young reader, and, 

 at the same time, to add considerably to his know- 

 ledge. There is a little too much of the goody-goody 

 style of writing about missionary enterprises, bu^ that is 

 the only point we are inclined to criticise. Tales of the 

 torturing of converts and murdering of ir.issionaries are 

 apt to create in children a morbid state not at all 

 desirable, and they can very well be omitted without 

 making a work on geography any the less interesting. 



LETTEKS TO THE EDITOli. 

 YTke Editor does not hold hifmetf responsible for opinions rx- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond' with the -writers of, rejected 

 manuscripts intended for this or any other part of NATURE. 

 No notice is taken of anonymous communications.'] 



Trituberculy and Polybuny. 



In' all the speculations on the original type of the mammalian 

 molar, beginning from Kuiimeyer (1863), we find that a simple 

 cusp or cone is, with perfectly logical reasoning, considered to 

 be the primitive form from which all others are derived. The 

 error, fatal in its consequences, consisted in the fact that all the 

 iceth possessing such a simple form, whether recent or fossil, 

 high or low in the system, have for a long time likewise been 

 considered 10 he primitive ; .'<o that the only problem remaining 

 10 be solved, seemed to be to trace hack the intermediate stages 

 between the more or less complicated molars of recent mammalia 

 and the '' .simple reptilian cone." 



The cretaceous deposits having long failed to throw light upon 

 the obscure reialions between the comparatively scanty mesozoic 

 mammalian teeth anrl the tertiary and existing forms, we were 

 reduced to make the best of the oldest tertiaiy faunas. It is 

 from the discovery of the lower eocene Puerco beds that the 

 establishment of the triluhcrcular theory dates, Cope having 



traced the superior molars of placentalia to a " tritubercular," 

 and their inferior molars to a " tubercular sectorial " type, both 

 of which he found to be of overwhelming preponderance in the 

 Puerco beds, the oldest known deposits of tertiary mammalia. 



I have elsewhere • raised objections to the inferences drawn 

 from the Puerco fauna, and now one of the most strenuous de- 

 fenders of trituberculy has, with his own hands, undermined 

 ihe stronghold of the theory, by denying the Puerco fauna the 

 claim to he in ancestral relaiion with later faunas, for he con- 

 siders this old fauna to be merely " an independent radiation of 

 placenials, like the Australian radiation of marsupials. "- 



Owing especially to the perseverance of Prof. Marsh, cre- 

 '' taceous mammalia were discovered in due time. The principal 

 characters of iheir molars can be grasped at once by a single 

 glance at the two beautiful and highly instructive plates pub- 

 lished hy Prof. Osborn, in December last.' 



Whoever examines with an unbiassed mind the molars figured 

 in the latter plate, must receive the impression that the term 

 " triiuberculate " applied lo them can stand only upon ihe Incus 

 a /ion luiciido \)Tinc'i[i\e. Speaking for myself, I cannot consider 

 to be tritubercular, molars which consist of from five to ten 

 tubercles ; therefore the teeth represenied on PI. viii. in my 

 opinion are polybunous (mullilubercular,\ as well as those of 

 PI. vii., though in a different manner. Prof. Osborn informs 

 us that the former " include a variety of forms just emerging 

 /rom the primitive tritubercular stage" (the italics are mine\ 

 "lending overwhelming proof, if any more were needed, of the 

 unity of origin of the molar types of the higher mammalia, from 

 a tritubercular stem instead of from a multiiubercular, as 

 Forsyth Major has suggested."* I suppose that by "primitive 

 iriiuhercular molar'' we are intended to understand a molar 

 which is in fact tritubercular sensu strenuo, namely, composed 

 of no more and no less than three cusps arranged in a triangle ; 

 but I fail to discover in the pages which follow the above 

 quotation, the proofs for the various assertions it contains. 



In order to explain why for such complicated molars as those 

 on the precited PI. viii, the designation tritubercular is main- 

 tained, it must be recorded that this name is said to be meant 

 to imply that the two outer cusps (paracone, metacone) and the 

 single inner one (protocone) in upper molars, as well as the 

 three anterior cusps (two inner and one outer) in lower molars, 

 generally the best developed of all the cusps, are to be con- 

 sidered as typical, primitive ; whilst the remainder, namely, the 

 intermediate and all the others of superior molars supposed 10 

 play a subordinate part, as well as those composing the heel of 

 inferior molars, are considered to be later additions to the crown. 



It has not, however, been shown, and I deny, that the pre- 

 dominant cusps have alway.s been such, and that the inter- 

 mediate ones, as well as the inferior heel (talonidj, are of later 

 origin than the former, and have always been in a subordinate 

 position with regard to them. Without searching farther than 

 what is to be seen on PI. viii., I state that the figures F are not 

 in favour of the assumption that two of the supposed primitive 

 cusps, the paracone .ind metacone, are always the best deve- 

 loped ; externally to them, we have here two superadded cusps, 

 ihe "parastylc" and " metaslyle," ■' which are in a much belter 

 Mate of development than the reduced two " primitive " cusps. 

 The latter, as the other figures of the plate suggest, may only 

 gradually have acquired their predominance by supplanting 

 ihe "styles, ' which in other patterns have become more or less 

 obsolete. On the whole, the superior molars of these " tri- 

 tubercular" cretaceous mammalia can best be compared with 

 those of Didelphyid,!-, as was done by Marsh, or to speak more 

 guardedly, rather with the Polyprotodontia in general, the 

 principal differences between ihe two consisting in the fact that 

 the cretaceous forms are more complicated. 



From the seemingly subordinate condition of the "heel" of 

 lower molars, as compared with their anterior portion, it does 

 not follow that the former is of later origin ; the difference 

 letween the two in vertical extension obviously depends on one 

 or more of the cusps of the so called trigonid having secondarily 

 become more elongated, for brachydoniy and not hypsodonly is 

 the original condition. If the heel were a later addition to the 



1 P./^.S. 1E93, p. 198-199. 



*- H. F. 0»born, "The Rise of the Mainm.ili.-i in North America," 

 pp. ^0-31. (Boston. 1S93.) 



■' H. F. Osborn, " Fo&sil MammaUor the Upper Ciruceous Beds." (Bull. 

 Am. Mils. Xal. Hist. v. 1893, pp. 311-330, pi. vii. .viii.) 



* / c. p. 320. 



^ Of their homoIoKucs, by the way. may Ik found trace.s in the molars of 

 many exivting mammals ; see e.g. If. Winge, Cm Pattedyrcnes Tandskifte 

 1882, Table 111 



NO. 1 283, VOL. 50] 



