12 



NATURAL HISTORY OF THE PRIMEVAL WORLD. 



All the existing genera of the marsupial order, both 

 herbivorous and carnivorous, are now peculiar to North 

 and South America, and to New Holland, with the 

 adjacent islands. The name Marsupialia is derived 

 (as we shall hereafter more fully explain) from the 

 presence of a large external marsupium, or pouch, 

 attached to the abdomen, wherein the foetus is placed 

 after a very brief period of uterine gestation, remaining 

 suspended to the nipple by its mouth, until sufficiently 

 matured to come forth to the external atmosphere. 



This order occupies an intermediate place between 

 oviparous and viviparous animals. Hence it naturally 

 formed a link between the Reptiles and the Mammals. 



It is interesting to observe, as Professor Owen re- 

 marks, that the Marsupials present a very complete 

 series, adapted to the assimilation of every form of 

 organic matter ; and no doubt they possessed a suffi- 

 ciently powerful instinctive precaution to preserve them- 

 selves from extermination, when surrounded with 

 enemies of no higher intellectual capacity than the 

 Reptilia. 



The Permian period closes what may be called the 

 Primary Epoch of our world, when it was appropriated 

 chiefly to animals living in the waters, and, especially, 

 to crustaceans and fishes. As we have seen, the forms 

 of the Reptilia were few in number, and of the Mam- 

 malia only one genus had appeared. We now arrive 

 at the Secondary Epoch, which, before all things, was 

 the epoch of reptile life. 



ANIMAL LIFE IN THE SECONDARY EPOCH. 

 The Secondary Epoch is subdivided by geologists 

 into three periods : 1. The Triassic ; 2. The Jurassic ; 

 3. The Cretaceous. 



THE TRIASSIC PERIOD. 



The Triassic period is so named because the rocks of 

 which it is composed, and which are more extended in 

 Germany than in England or France, were denomi- 

 nated the trias or triple group by German writers. 

 They form, in fact, three groups, which, in ascending 

 order, are as follows : 



Neic Red Sandstone. In this new phase of the 

 revolutions of the globe, says a recent writer, the 

 animated denizens of its surface differ greatly from 

 those summoned into existence during the Primary 

 Epoch. Those curious crustaceans, the Trilobites, 

 have disappeared ; the Cephalopods and Brachiopods 

 have dwindled in numbers; the ganoid and placoid 

 fishes gradually decline, and finally become extinct. 

 But the life of the Ammonites now begins, and attains 



at once to a surprising development. In like manner, 

 while some genera of terrestrial animals have passed 

 away, others now, for the first time, " live, move, and 

 have their being." The huge Chelonians now surge 

 through the seas, and bask in the sunshine on the 

 borders of the great lakes. The saurian reptiles assume 

 colossal proportions, preparing the way for those yet 

 more gigantic Saurians which belong to the follow- 

 ing period, and whose enormous skeletons and laidly 

 aspect excite the awe and astonishment of all who gaze 

 upon their marvellous remains. 



Few animal relics, however, are found in the Bunter 

 sandstone, although it bears numerous traces of the 

 Labyrinthodon. 



The Muschelkalk is so named from the multitude of 

 shells which it embodies, and of which, in truth, it 

 consists; including vast numbers of Molluscs, twelve 

 different genera of saurian reptiles, some Cheloniae, or 

 turtles, and six new genera of cuirassed or armour- 

 plated fishes. 



Let us pause, for a moment, to gain some conception 

 of the molluscous varieties. 



The Brachiopods are still represented by Terebratula, 

 Lingula, Spirifer; 



The Conchifcra, by Trigonia, Mya, Flngiostoma, 

 Ostrea, Airicula; 



The Gasteropods, by Turbo, Tw-ritella, Buccinum, 

 Natica, RosteUaria ; 



The Cephalopods, by Ceratites, Nautilus, Belemnite, 

 Rhyncholite, Orthoceras. 



The Mytilus, or Mussel, which properly belongs to 

 this sub-period, is the acephalous (or headless) Mol- 

 lusc, with elongated triangular shell, of which many 

 species inhabit our existing seas. Other acephalous 

 Molluscs of the same time were the Lima, Myophonia, 

 Posidonia, and Avicula. 



Among the Cephalopods we select the Belemnites 

 as worthy of more particular notice. They differ from 

 other fossil chambered shells in having their chambers 

 inclosed within a cone-shaped fibrous sheath, resem- 

 bling in form the point of an arrow, whence they derive 

 their name. 



A Belemnite may be described as a compound inter- 

 nal shell, consisting of three essential parts : 



First, a fibro-calcareous cone-shaped shell, termi- 

 nating at its larger end in a hollow cone. 



Second, a conical thin horny sheath, or cup, com- 

 mencing from the base of the hollow cone of the fibro- 

 calcareous sheath, and rapidly enlarging as it extends 

 outwards to a considerable distance. This cup-like 

 sheath formed the anterior chamber of the Belemnite, 

 and contained the ink bag and some other viscera. 



Third, a thin conical internal chambered shell, called 

 the alveolus, placed within the hollow calcareous cone 

 already described. 



This portion of the shell is closely allied in form and 

 construction to the Nautilus and Orthoceratite. Thin 

 transverse plates divide it into a series of narrow air- 

 chambers, or areola, resembling a pile of watch-glasses, 

 gradually diminishing towards the apex. Outwardly 

 these plates are concave, inwardly convex ; and a con- 

 tinuous siphuncle, or locomotor tube, runs through all 

 of them. 



