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Show 116 HYPOTHESIS (IF THE DEVELOPMENT OJ" prece~ing. illustrations in a form calc:ulated to bri11g them. !llore. forc1bly before the mind of the reader. The followmg table was suggested to me, in consequence of seeing the ~cale of animated nature presented in Dr. F~etche(s ~ud1ments of Physiology. Taking that scale as Its basis, It shows the wonderful parity observed in the progress of creation as presented to our observation in the succession of fossils, and also in the fretal progress of one of the prin .. cipal human organs.* This scale, it may be remarked, was not made up with a view to support such an hypothesis as the present, nor with any apparent regard to the history of fossils, but merely to express the appearance of advancement in the orders of the Cuvierian system, assuming, as the criterion of that advancement, '' an increase in the number and extent of the manifestations of •. 11 It is a fact of the highest interest and moment that as the bram ~f every tr~be of animals appears to pass, during its devclopmm! t, m successiOn through the types of all those below H, so the hram. of man passes through the typ~s of those of every tribe in the creatJOn. I~ represents, accordingly, before the second month of utero-gestation, that of an avertebrated animal; at the scconu month, that of an os~eous fish; at the third, that of a turtle ; at the fourth, that of a bird : at the fifth that of one of the rodcntia · at the sixth., ~~~at of one of the ruminantia; at the seventh, that of o.ne of the digibgrada; at the eighth, that of one of the q uadrumana · till at length, at the ninth, it compasses the brain of MaH ! Jt i~ hardly nece~sary to. say, that all this is only an approximation to the truth; smc.e ~either is the brain of all osseous fi shes, of all turtles, of all I.Hrds, nor of all the species of any one of the above ord~r of mamals, b):" any means precisely the flame, nor does the bram of the. hu.m.an frotus at any time precisely resemble, perhaps, that of al_ly md!vidua~ whatever among the lower animals. Nevertheles~, It may be sa1d to represent, at Pach of the above.mention- " e~ penods, t~e ag~rc.gate, ~- it were, of the brains of each of the ti!bes state.d , cons1stmg as It does, about the second month, chiefly oi the !DPSI~l. part~ of the r.erebcllum, the corpora quadrigemina, thalami opt.ICI, rud1ments of the hemispheres of the cerebrum and C?rpora str1ata; and receiving in succe. sion, at the third, the ru~ un~nts of the lobes of the .cerehrum ; at the fourth those of the forrux, corpus callosum, and septum luci<1um · at the fifth . the tu· bor u?nul~r·e, and so forth the posterior lobes' of the ceret)rum in ~~easmg from before to behind, so as to cov r the thalami optici . ~ut the fourth month, the corpora quadrig<·mina at Jnt the sixth :~1 the ccre?ellum a~ lout the seventh. This, then, is another ex , ple ~~ ar~ mcreas.e m tlw complexity of an organ sueceeding Hs centraln. at10~; as 1f nature, having fir, t piled up her materials in .)ne SI~ot, del1gl~tf'd afterwards to employ her abundance not so r11lCh 11~ enlargmg old parts as ll\ forming new ones upor{ the old ,~undatwns, aad thus adding to the complexity of a fabric tlw ru• ~~~t11 ta~ stru~ture of which is in all animals equllly simple"· - .r tete tel's Rudtrn,nts of Physiology. • THE VEG:E'l'ABLE AND ANIMAL KINGDOMS. 117 life, or of the relations which an organized bein()' bears to the external. world." Excepting in the relative 0 situation of ~he annelida and a few of the mamm~l orders, the parity Is perfect; nor 1nay even. these small discrepancies appear when the order uf fossils shall have been further in vestigated, or a more correct scale shall have been formed. Meanwhile~ it is a wonderful evidence in favor cf our hypothesis~ that a scale fermed. so arbitrarily should coincide to such a nearness with our present knowledge of the succession of animal forms upon earth, and also ~hat both of these series should harmonize so well with the view given by n1odern physiologists of the embryotic progress of one of the organs of the ,highest order of animals. The reader has seen physical couditions several times referred to, as to be presumed to have in some way gov~ rned the J?rogress of the development of the zoological circle. This language may seem vague, and, it may be ask~d-:-can any :particular physical condition be adduced as ·hkely to have affected development? To this it may be_ an~wered, t~at air ar:d l!gh~ ar.e probably amongst the pnncipal agencies of this lnnd whiCh operated in educing t~e various forms of bei.ng. Light is found to be essen-/\ 1.. () c,.(l hal to the development of the individual embryo. \Vhen tadpoles were placed in a perforated box and that box sunk in the Seine, light being the only co~dition thus ab-stract. ed, they grew to a great size in their original form, bu.t d1d not pass thFough the usual metamorphose which bnngs them to then mature state as froo·s. The proteus an animal of the frog kind, inhabiting the subterraneou~ waters of · Ca!·niola, and which never acquires perfect 1 ungs so as to become a land animal, is presumed to be an exa~npl~ of arrested development, from the same cause. When, In connexion with these facts, we learn th~t hu-man ~others liviJ.?-g in da~·k and close ~ells under ground, t~at Is to ~ay, with an Inadequate provision of air and hgh.t-are _found to produce an unusual proportion of de-fectt ve children,* we c~n appreciate the important ef-fects. of both these ph~'Slcal ~onditions ~n ordinary repro-ductwn. Now there 1s noth1.ng to forbid the supposition that the earth has been at different stages of its career ,. Some poo~ pe~ple h~vi_ng taken up their abode in the eells Hnder the fortificatiOns ot Lisle, the proportion of defective infants pr~dune.d by them became so great, that it was deemed necessa1-y to 1ssue an order commanding these cells to be shut up • |