3o8 



NATURE 



\Feb. 17, 1876 



this condition are seen in the Marsupials, and in a still 

 higher degree in the small order of Monotremes. These 

 present a marked approach to the Sanropsida, or reptile 

 and bird group. Such semi-transitional forms, as they 

 may be called, furnish valuable indications of the route 

 by which the higher types might have been brought 

 about, and appear, upon the evolutionary hypothesis, to 

 be unmodified survivors of a condition which was only 

 transitory in the large bulk of the class. Their value as 

 evidence for gradual development would be greatly 

 strengthened if corroborated by palaeontology. Beyond 

 them nothing is known in the present condition of life of 

 any truly intermediate forms between the Mammalia and 

 the other class of vertebrates, and the same must be said, 

 as far as we know at present, of all former ages. The 

 line which we now draw round the class to separate it from 

 all others will include within its limits all hitherto disco- 

 vered mammalian remains. No forms more transitional, or 

 approaching nearer to any other class, or even, as we shall 

 see, so near as do the Monotremes, occur in the records 

 of palaeontology. Of course our evidence on the subject 

 is only negative, and as such has little real value. The 

 first appearance, of which we are at present informed, of 

 mammals upon the earth, was early in the Mesozoic 

 period, in the epoch called Triassic. At that time the 

 other classes of Vertebrata, except, perhaps, birds (but 

 our evidence here is defective), had long been well 

 established and distinctly defined. Indications of mam- 

 malian life occur in various formations, at different ages, 

 and at scattered points upon the earth's surface, through- 

 out the Mesozoic ages, but during its later stages are 

 entirely lost. These indications, though very frag- 

 mentary, all show animals of minute proportions, and for 

 the class to which they belong, rather low organisation. 

 With the commencement of the Tertiary period, however, 

 a total change takes place. Wherever the great Cretaceous 

 ocean bottoms have been elevated so as to become the fit 

 habitation of terrestrial animals, there mammals of varied 

 size, form, and function have been found to dwell, and 

 have left their remains, and from henceforth to the pre- 

 sent lime there is abundance of evidence of their con- 

 tinuous occupation of the earth's surface. The total 

 absence of all marine mammals in the Cretaceous epoch, 

 the fauna of which is, on the whole, so well preserved, 

 and the absence of land mammals in the Wealden, are 

 facts, which though difficult to account for, must not be 

 overlooked. 



Before proceeding to the consideration of the history of 

 the special groups of Mammalia, attention may be called 

 to a few points of general interest relating to the whole 

 class, in which palseontological researches appear to have 

 shown some evidence of gradual modification or progres- 

 sion as time advanced. The first is a small point, as it 

 relates only to one family of animals, but it affords a good 

 illustration of the parallelism which has been observed 

 between the development of the race and that of the indi- 

 vidual. The earliest known forms of deer, those of the 

 Lower Miocene, as remarked by Gaudry, have no antlers, 

 as the young of the existing species. The deer of the 

 Middle Miocene have simple antlers, with not more than 

 two branches, as in existing deer in the second year. In 

 the Upper Miocene, species occur with three branches to 

 the antlers, but it is not until the Upper PHocene and 

 Pleistocene times, that deer occur with antlers deve- 

 loped with that luxuriance of growth and beauty of form, 

 characteristic of some of the existing species in the 

 perfectly adult state. Next, the teeth in the greater 

 number of Eocene mammals, both herbivorous and carni- 

 vorous, were of a much more generalised character than 

 at present, and, as shown by Owen, commonly presented 

 the full typical number of three incisors, one canine, four 

 pre-molars, and three molars in each side of each jaw, 

 making forty-four in all, a number found only in two 

 genera at present existing. These teeth, moreover, in 



many species were more uniform in character and regu- 

 larly placed, without intervals, in the jaws than in most of 

 the later forms. They were also usually very short- 

 crowned, and many cases can be traced of a successive 

 lengthening of the crowns of the molars, and consequent 

 greater provision for the wear of the organ, in a closely 

 allied series of animals passing through successive geo- 

 logical epochs. Lastly, as remarked first l)y Lartet, and 

 subsequently by Marsh, there has been in many groups a 

 gradual increase of the size of the brain, as ascertained by 

 the capacity of the interior of the cranium. Most of the 

 Eocene mammals had very small brains in proportion to 

 their size ; this is well exemplified in the earliest known 

 European Eocene carnivorous mammal, /Uxtocyon pri- 

 incevus, and still more strikingly in the huge American 

 Dinocerata, animals nearly as large as the existing 

 elephants, but whose brain cavity more resembles that of 

 a reptile, being not more than one-eighth the capacity of 

 that of a rhinoceros. The Miocene mammals of the 

 same country had better developed [brains, but even in 

 the Pliocene Mastodons they did not equal the existing 

 Proboscidea. A similar progression of brain capacity has 

 been observed among deer, among the tapiroid Ungu- 

 lates, and in a very well marked manner among equine 

 mammals, especially from the Eocene Orohippus, through 

 Miohippus ^ndi Anchitheriuni of the Miocene, Pliohippus 

 and Hipparion of the Pliccene, to the recent Equus. 



{To be continued.) 



MADAGASCAR' 



A S most probably many of our readers know, a wealthy 

 ■^"^ Parisian, M. Alfred Grandidier, who is thoroughly 

 acquainted with Madagascar in all its aspects, has under- 

 taken a mighty work on the physical, natural, and 

 political history of the island, which is to form, when 

 completed, twenty-eight volumes in large quarto, pro- 

 fusely illustrated with coloured plates. Six volumes, three 

 of text and three of plates, are to be devoted to the 

 Mammals, the first of each of these being those under 

 notice on the present occasion. They, together with the 

 Birds, in three volumes, and the Crustacea, are under the 

 editorship of M. Alph. Milne-Edwards. The Fishes are 

 undertaken by Dr. Sauvage ; the Reptiles by M. Gran- 

 didier ; the Insects by MM. Kunckel d'Herculais, Lucas, 

 Oustalet, De Saussure ; the Annelids by M. L. Vaillant, 

 and the Mollusca by MM. Fisher and Crosse. 



In the volumes before us there are 122 plates de- 

 voted to the anatomy of the Lemurian family Indrisincs. 

 Propithecus diadema, P. edivardsii, P. verreauxii, P. 

 deckenii, P. coquerelii, P. coronatus, Avahis {Micro- 

 rhynchus) laniger, Indris brevicaudatus are the species 

 figured. Of these plates, thirty-nine refer to their osteo- 

 logy, more than twenty to their myology, forty to their 

 visceral anatomy, thirteen to their external form, and 

 twelve (as photographs) to the configuration of the feet. 

 Most of these plates are exquisitely coloured, and all are 

 beautifully drawn ; the livers being the only organs with 

 which we have any fault to find. The volume of letter- 

 press only extends as far as the myology, the account of 

 the viscera not having yet appeared. It is to do so in 

 March next. From the drawings alone many particularly 

 instructive facts may be learnt. The colic caecum of 

 Propithecus is seen to be comparatively short and capa- 

 cious, at the same time that the helix formed by the con- 

 volutions of the colon itself is as considerable as in any 

 ruminant animal. In Avahis the helix is much less 

 developed, whilst the caecum is longer. In Indris the 

 caecum is enormously long, not being wide, the colic 

 coil not forming a helix, but being disposed in parallel 



I "Histoire Physique, Naturelle et Politique de Madagascar." Publiee 

 par Alfred Grandidier. " Histoire Naturelle des Mammiferes." Par MM. 

 Alph. Milne-Edwards et A. Grandidier. Vol. VI. (texte) et Vol. IX. 

 (atlas). (Paris : Imprimerie Nationale, 1875.) 



