2l6 



NATURt: 



[August i8, 1910 



show points of much special interest. Prof. Wood suggests 

 various possibly useful applications of such methods. Prof. 

 R. Namias has examined prints toned with gold and 

 platinum to ascertain the amount of precious metal enter- 

 ing into the finished print. C. W. Gamble described a 

 method of determining the melting point of gelatine jellies. 

 He uses capillary tubes, and notices when the concave 

 meniscus changes to a flat surface. 



A. and L. Lumifere and A. Seyewetz classified and com- 

 pared the various gelatine-hardening agents, and recom- 

 mend the use of quinone and its sulphonic derivatives 

 when the gelatine is on a rigid support, in preference to 

 formalin, as the latter tends to contract the gelatine and 

 detach it. They find that quinones in acid solution are 

 serviceable for the reduction of photographic silver images, 

 and that their action is comparable to that of ammonium 

 persulphate in appearing to attaclc by preference the denser 

 deposits. They suppose that the resulting , hydroquinone 

 tends to deposit silver, by reduction from the solution, on 

 the surface, and so to prevent the loss of the thinner 

 deposits. 



A method for getting instantaneous exposures on auto- 

 chrome plates was described by Ch. Simmen. The plate 

 is sensitised to red by bathing, and with a suitable com- 

 pensation filter is eight times more sensitive than the 

 untreated plate. N. S. Amstutz reported on recent pro- 

 gress in process work in the United States of America. 

 We notice that Paynetype has not yet come into general 

 use ; that collotype has not made much headway, in spite 

 of the hopes of its adherents, presumably for lack of 

 attention to climatic conditions; but illustrative telegraphy 

 is taking its place as a practical method of transmitting 

 pictures. W. F. Cooper and G. A. Freak have compared 

 nickel (or nickel-surfaced plates) as a substitute for copper 

 for half-tone work, and find that ferric chloride acts on 

 it (for etching) at something less than half the rate that 

 it acts on copper. 



Telephotography is the subject of a report by Captain 

 Owen \\"heeler ; other than this, photographic optics was 

 hardiv represented. It will, of course, be understood that 

 in this summary it has not been possible to refer to more 

 than a comparatively few of the communications made to 

 the congress. C. J. 



THE ORIGIN AND CLASSIFICATION OF 



MAMMALS.^ 

 A H E.ARTY welcome may be accorded to the work 

 •^ referred to below, which contains a well-elaborated 

 and highly philosophical digest of the present state of our 

 knowledge of the past history and relationships of the 

 various groups of mammals, and the inferences which may 

 be legitimately drawn from such knowledge. The work 

 owes its inception to the need for a brief outline of the 

 history of the ordinal classification of mammals for use 

 in Columbia University ; but it was soon found inadvisable 

 to limit its scope to this portion of the subject, and it 

 consequently covers a much wider range. It retains, how- 

 ever, traces of its origin.al limitation in consisting of two 

 distinct parts, namely, an account of the typical stages in 

 the history of the classification of mammals, and, secondly, 

 of the genetic relations of the orders and a discussion of 

 the origin of the class as a Whole, with special reference 

 to the problem of the auditory ossicles. 



The first part, althoiigh of great value to the student, 

 may be passed over without further mention on this 

 occasion, and attention concentrated on the second. Before 

 proceeding to a brief survey of the latter, reference may be 

 made to the author's end'eavoui-s to give a rational explana- 

 tion of the meaning of each important feature with which 

 he has to deal, and not to rest content with a mere cata- 

 logue of bare facts. Indeed, the adherence to mere facts 

 on the part of so many of his predecessors has been, in the 

 author's opinion, a fruitful source of our lack of progress 

 in getting a real grasp of mammalian evolution, and he 

 specially urges the need of an osteological treatise written 

 from this newer point of view. It is added that the import- 

 ance of osteology in the study of mammals cannot be over- 

 estimated, as the clue to the origin of the class and the 



1 "The Orders of MammaU." By W. K. Gregory. Bull. Amer. Mus. 

 Nal. Hist., vol. xxvii.. 1910. Pp. 5^4. 



NO. 2129, VOL. 84] 



relationships of its constituent orders can be obtained from 

 palaeontology alone, which in this case is restricted to the 

 osteology and dentition. 



As regards the origin of mammals, Mr. Gregory adopts 

 the view that the class is descended in all probability from 

 that section of the anomodont reptiles which Dr. Broom 

 has proposed to designate cynodonts, but which are more 

 commonly included in the theriodonts, although not from 

 any known member of the same. The features in which 

 cynodonts approximate to mammals on the one hand and 

 to more ordinary reptiles on the other are carefully formu- 

 lated. The difficult question of the fate of the reptilian 

 quadrate and the homology of the mammalian malleus and 

 incus is left to a great extent open, although the author 

 seems inclined to favour the view that the incus represents 

 the quadrate and the body of the malleus the articular. 



The second chapter of this part is devoted to the mono- 

 tremes, which are regarded' as undoubted mammals, with 

 evident relationships to the marsupials, as is indeed 

 mdicated by their geographical distribution. Nevertheless, 

 monotremes are taken to represent a subclass by them- 

 selves, while marsupials and placentals are brigaded 

 together in a second group of equivalent value, and it is 

 added that the divergence of the monotreme from the 

 marsupio-placental stock must have taken place at a rela- 

 tively early date. Within the same section as the marsupials 

 are grouped, as a second and equivalent order, the Mesozoic 

 triconodonts, which cannot be regarded as true marsupials, 

 and it is noteworthy that the theory of the conversion of 

 the triconodont into the tritubercular type of molar by 

 means of torsion is now definitely abandoned. On the 

 other hand, in view of Gidley's study of Ptilodus, the Multi- 

 tuberculata are now re-admitted to the marsupial order, 

 although the author will not allow that they are diproto- 

 donts. The evidence of the Triassic Microlestes, supple- 

 mented by that of the structure of the teeth themselves, 

 indicates that the multituberculate molar is a far older 

 type than the tritubercular, which is first known — in an 

 incompletely developed condition — in the Middle Jurassic 

 .\mohitherium. 



The view that the carnivores of the Santa Cruz beds 

 are not only marsupials, but likewise members of the same 

 family as the Tasnianian wolf, is definitely accepted, and 

 it follows from this that there is no definite genetic relation- 

 ship between creodonts and carnivorous marsupials. 

 Indeed, the author considers each group to have been in- 

 dependently derived from small insectivorous and com- 

 pletely or partially arboreal Mesozoic forms, this being, if 

 true, sufficient to indicate that the resemblance between 

 the larger Tertiary forms is due to convergence. In opposi- 

 tion to some of his contemporaries, Mr. Gregory regards 

 creodonts as nearly related to the Insectivora (from which 

 tupais and jumping-shrews are separated as a distinct 

 order, Menotyphla), and likewise considers the latter to 

 be more closely related to marsupials than is the case with 

 any other placental group. On the other hand, he looks 

 upon the palatal vacuities of Erinaceus as secondary rather 

 than marsupial features. The date of separation between 

 Carnivora and Insectivora is considered to be pre-Tertiary, 

 and it is left an open question whether the ancestors of 

 the latter had their inci.sors extending along the sides of 

 the. jaw (instead of being restricted to the front) as in their 

 modern representatives. 



, Only very brief reference can be made to some of the 

 other orders, among which it is important to notice that 

 the extinct zeuglodonts are included in the Cetacea. 

 Perhaps the greatest changes in classification are proposed 

 in the case of the ungulates, from which the Artiodactyla 

 are removed to form a separate ordinal, and supraordinal, 

 group, as the author believes they have no near relation- 

 ship with Perissodactyla. On the other hand, the Ungulata 

 are taken to include, not only elephants, hyraxes, perisso- 

 dactyles, and the South American groups, which are 

 brigaded as Notoungulata, but likewise sirenians. Much 

 is to be said both for and against these proposed changes, 

 but space does not admit of discussing the matter, and it 

 must suffice to add that we find the Primates, with man 

 at the head, forming part of a " superorder " in the middle 

 of the class instead of standing at the head. W'hether we 

 accept all his views or not, there can be no question that 

 in this volume Mr. Gregory has accomplished a most 

 valuable and important piece of work. R. L. 



