2 



NATURAL HISTOKY OF THE PKIMEVAL WORLD. 



for its last an J greatest iiiliabitaut — Man. He will see, 

 moreover, a constaat succession of forms of animal life 

 rising from lower to bigher organizations; not so much, 

 it is true, by tlie law of development as by that of sub- 

 stitutiun. Yet he will observe, too, a certain measnre 

 of development. It may not be correct to say that the 

 trilohite has developed into man, but it is certain that 

 all man's parts and organs— to use Professor Owen's 

 expression— have been "sketched ont" in anticipation 

 in the inferior animals. All those creatines which lived 

 and died in the bygone ages of the primeval world lived 

 and died in pre-ordained preparation for the embodi- 

 ment of the "divine Archetype" in his precious "ves- 

 ture of humanity." Thus, then, to the naturalist, Man 

 must ever appear as the apex of creation, the most 

 perfect form of animal life, the " centre of the universe 

 of time." 



PraMARY EPOCH. 



The tirst forms of life upon the surface of our planet 

 would seem to have been vegetable ; the earliest animal 

 organisms belong to the Silukian Period.* The earth 

 was then covered with seas of no great depth, whose 

 waters eddied round isolated rocks, or seethed over 

 barren submarine reefs ; rocks and reefs being clothed 

 with flowerless Ahx, among which various species of 

 Molluscs found an asylum and a provision. 



These molluscs belonged to the group Birichiopoda, 

 or arm-footed ; a group with bivalve shells, differing 

 in internal structure from most recent bivalve molluscs. 

 In these the mantle, or jxilliiw), consisted of two broad 

 expansions or lobes, which shut in the soft body of the 

 animal. The processes of respiration and aeration of 

 the blood were carried on by the surface of the lobes, 

 which were covered with a labyrinth of minute blood- 

 vessels, and fringed along the edges with vibratory cilia. " 

 By means of the cilia the animal maintained a constant 

 motion in the surrounding water, which provided it 

 with the necessary supplies of fresh air. It procured 

 its food through the agency of a singular apparatus ; two 

 long tremulous arms, which, proceeding from the sides 

 of its mouth, were furnished with a host of filaments 

 to entangle as in a mesh its prey. 



Among the fossil remains of this period the genus 

 Lingula is especially abundant. It is the only bivalve 

 with a pedunculated shell; that is, the only bivalve 

 able to attach itself to external objects by means of a 

 hollow fleshy tube, called a pedimcle. It had two long 

 ciliated arms, like its congener, which it curled up during 

 repose. Its shell was thin, with equal valves, of a horny 

 or calcareous character, peaked at the apex, and gener- 

 ally open at the base. 



This genus is represented in the islands of the Indian 

 seas by several existing species. 



In the Silurian strata, and, indeed, in all Palsozoio 

 rocks up to the Triassic, are found numerous remains of 

 a genus of molluscs which pala;ontologists have named 

 Orthoceras, straight-horn. In many respects it is 

 closely akin to that fairy-like tenant of the existing seas, 

 the Nautilus, and might not inaccurately be described 



• So caltrd because the str.ita compnsin^ it were discovered 

 on nn exteusive scale, by Sir Hodeiielt JIurchison, in that part of 

 Wales formerly inhabited by the Silures. 



as a nautilus unrolled and stretched out straight. It 

 has a straight shell, and its interior compartments are 

 separated by thin partitions, and pierced by a cylindri- 

 cal tube or siphuncle. According to tlie form and size 

 of this siphuncle the Orthoceratites have been classitied 

 into certain sub-genera, including nearly 200 species. 

 Theyare very widely distributed, and of all the paIa;ozoic 

 fossils are the most abundant. In the Silurian seas they 

 lived a life of piracy and rapine, preying upon other 

 animals, which they hunted into the profoundest recesses, 

 and strangled in the tenacious grasp of their long arms. 



The Ortliis (straight) is a genus of fossil braoliiopods, 

 also found in tlie Silurian rocks, and including upwards 

 of 100 species. 



To tlie same period belongs the genus Tcrchratula, 

 of which only one living species exist, but the fossil 

 are more than 100 in number. The animal was 

 attached to its smooth circular shell, which had a trun- 

 cated and perforated beak, by a pedicle ; and the animal 

 itself consisted of a kind of slender, flattened, calcareous 

 loop, with divergent pieces, and a ciliated appendage on 

 either side. The shell is covered with minute perfora- 

 tions, and frequently ribbed in a very curious manner. 

 It bears a general resemblance to that of the cockle, so 

 plentiful on our British shores. 



The only family o'i Crustaceans created in the Silurian 

 period was that of the Trilohites, first described, upwards 

 of a century ago, by Edward Lhuyd, then curator of 

 the Asbmolean Museum at Oxford. 



They appear to have moved only by swimming, and 

 to have lived very near the surface of the water. When 

 in locomotion they preserved an inverted position, with 

 the belly upwards, and on the approach of danger imme- 

 diately rolled themselves up into a ball, like the hedge- 

 hog. They haunted the vicinity of the low marshy 

 coasts, where they lived gregariously in countless 

 legions, feeding on the smaller water-animals. Bur- 

 meister, whose monograph on this order is remarkable 

 for closeness of observation and lucidity of statement, 

 considers their nearest type, in the present seas, to be 

 the Entomostraceous Crustacea known as the PliyUapoda. 



Their body was covered with an ingeniously-jointed 

 shell, in which, says Figuier, the mediaeval armourer 

 might have found all his contrivances anticipated, with 

 not a few besides which his invention failed to discover. 



The head was protected by an oval shield ; the body 

 composed of a certain number of rings or segments ; 

 the tail of many closely-filted joints. The eyes were 

 sessile and compound, and of remarkable magnifying 

 power; the lens in one species, Asaphus caudatus, con- 

 sisting of fully 400, and in another, Asaplms tyrannus, 

 of at least 6000 facets. This extraordinary strength' of 

 vision was doubtless requisite to reveal to them the 

 minute aquatic organisms on which they preyed. * 



* In reference to tlie eyes of the Triliibites, Dr. Biickland has 

 some very just and interesting observations. He points out that 

 the waters wherein they maintained their existence throni|;hout 

 the entire period of tlie Transition formation, could not have 

 been that imaginary turbid and compound chaotic fluid, from the 

 yirecipitates of which some geologists have supposed the materials 

 of the surface of the earth to be derived; because the structure 

 of their eyes is such, that any kind of fluid in wliich they could 

 have been efKcient at tlic bottom, must have been pure and trans- 

 parent enough to allow the passage of light to organs of vision. 



