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Show 246 EXPLAN ATIO.NS. s':lggested that the peculiar organization of the rr.arsu. ptals points to their having been derived through a dif~ ferent medium from other mammals. The critic, eager to let nothing escape, tells us that there are other land mammals lower in organic type than the marsupials. One answer to this objection might be found in an explanation of my views respecting the ornithic descent of the~e an.imals; but I am. unwilling to pause upon such an 1nfenor matter, and will therefore meet him with the question, if any other mammals shoV\~ that lowly grade ot organization which is marked by the absence of a pla~ enta l . '' There are no othe~ organic types," he says, " to whtch they (the marsupials] offer the shadow of a near affinity. They are therefore in direct antao-onism with the scheme of regular development." To this it m~y be replied, that t~e affin~ty of the marsupials to the ov!parous ver~ebrata IS adr~ntted by every naturalist, being shown In the small SIZe of the brain and consequent exposure of the cerebellum, the absence of the s~ptum lucidum and corpus callosum in the brain, and various other traits. Professor Rymer Jones, of King's College, whose testimony on such a point will be admitted by the reviewer, speaks of the Inarsupials as " connecting links between the oviparous and placental vertebrata." Striking traits of their affinity to birds are shown, he says, in the structure of the ear and of the reproductive organs.* In reality, the whole figure of the cursorial bird, the small head upon the long neck, the extreme length of the hinder limbs, and the imperfect development of the fore extremities, as well as the tendency of the feathers to a hair-like character, speak irresistibly for its approach to certain marsupials. The ornithorhynchus is as clearly an advance from the natatorial bjrd towards the rodent form, the latter being an order whose osteological structure is allowed by every naturalist to be bird-like. New and curious illustrations of the connection between the birds and the implacental mammalia arc constantly appearing. We lately heard of a bird which has a pouch for its young like the kangaroo, t and Mayer has d1scovered in the female cmeu a purse form of certain organs, indicating an approach to the marsupial in that part of structure which is the Inost Jis· • General View of the Structure of the Animal Kingdom. 1 Magazine of Natural History. TER 'll A:R. Y FOSSILS. 247 !in~hve in. the case.* J~ would appear that the reviewer IS s1m~ly tgnorant of this derartment of natural history, and, with the self-esteem which o~ten attends upon ignorar!. ce, he has somewhat unluckily ventured to give a positive co~tradiction to that which is incontestably true. The reviewer at length comes to the organic phenomena of the Tertiary system. "On the theory of development," says he, '' ' the stages of adva-nce are in all cases very small-from speoies to species,' and the pheno~ ena, 'as shown in the pages of geology, are always of a simple and modest character.' Let us test these assumptions by one single step, from the chalk to the Lon~ on clay, or a~y other tertiary deposit. Among the milhons of organic forms, fro1n corals up to mammals we find hardly. so ~uch ~s one sing~e secondat·y speci'es." The exceptwns 1n reality are, the Infusoria of the chalk and " two or three secondary species," which are said t~ ~'straggle ~nto the tertiary system." "Organic nature," he sa.ys, " Is once more on a ne":' pattern-plants as well lS animals are changed. It mtgh t seem as if we had Jeen transported to a new planet; for neither in the arfangement of the genera and spectes, nor in their affinities "Vith the types of an older world, is there the shadow of my a~proach to a regular plan of organic development., ~ow .. h~ almost total break in the organic creation here i:-lsistcd uoon occurs in the interval between the exten- 4ive d.eposlts of the secondary forrnatio n and the comparativ~ ly isolat.ed dep?sits of the tertiary. It is an interval which the lithologiCal arrangements clearly indicate to have been longer than ·any of those between the other formations, during which minor chan{Tes of oro·anic creation had taket1 place. It is simply, then, a 0period not t·epresented by strata or by fossils; while it elapsed, the co~tinual a~vance of the organic wot:ld proceeded to a point at whiCh nearly all the old species had died out or been ch.anged. Ther~ was nothing more in the "step " of our reviewer than this Such is the geological doctrine. "Is the present creation of life," says Professor Phillips "a continuation of the previous ones; a term of the sam~ lo:1g seri.es of communicated be~ng l I answer, ye~."t '' There Is no break," he says, "1n the vast chain of or- .. Reports of Ray Society, I. t He adds-" But not as the offspring ii a continuation ot the parent." |