INVERTEBRATA, CRYPTOGAMIAj MICROSCOPY, ETC. 595 



•wHch these new organs have been little by little called into being. 

 At the same time, here and tliere along the line of march, certain 

 forms have been supposed to have " fallen out " — to have ceased to 

 improve ; and being happily fitted to the conditions of life in which 

 they were long ago existing, have continued down to the present day 

 to exist in the same low, imperfect condition. It is in this way that 

 the lowest forms of animal life at present existing are usually explained, 

 such as the microscopic animalcules, Amoehi^ and Infusoria. It is in 

 this way that the lower or more simply-made families of higher 

 groups have been generally regarded. The simpler living Mollusca 

 have been supposed necessarily to represent the original forms of the 

 great race of Mollusca. The simpler vertebrates have been supposed 

 necessarily to represent the original vertebrates, and so on. 



That this is, to a certain extent, a true exjilanation of the existence 

 at the present day of low forms of animals is proved by the fact that 

 we find, in very ancient strata, fossil remains of animals whicli difter 

 over so little from particular animals existing at the present day; 

 for instance, the Brachiopods Lingula and Terehraiula, the king- 

 crabs, and the pearly nautilus are found living at the present day, 

 and arc also found with no appreciable difference in very ancient 

 strata of the earth's crust, deposited so long ago that most of the 

 present forms of life had not then been brought into existence, wliilst 

 other most strange and varied forms occupied their place, and have 

 now for long ages been extinct. 



Whilst we are thus justified by the direct testimony of fossil 

 remains in accounting for some living forms on the hypothesis that 

 their peculiar conditions of life have been such as to maintain them 

 for an immense period of time in statu quo unchanged, loe have no 

 reason for applying this hypothesis, and this only, to the explanation of 

 all the more imperfectly organized forms of animal or plant life. 



It is clearly enough possible for a set of forces such as we sum up 

 - under the head " natural selection " to so act on tlie structure of an 

 organism as to produce one of three results, namely these : to keep it 

 in statu quo ; to increase the complexity of its structure ; or lastly, to 

 diminish the comiilexity of its structure. We have as possibilities 

 either halance, or elaboration, or degeneration. 



Owing, as it seems, to the predisposing influence of the systems 

 of classification in ascending series proceeding steadily upwards from 

 the " lower " or simplest forms to the " higher " or more complex form 

 — systems which were prevalent before the doctrine of transformisni 

 had taken firm root in the minds of naturalists — there has been up to 

 the present day an endeavour to explain every existing form of life on 

 the hypothesis that it has been maintained for long ages in n state of 

 balance ; or else on the hypothesis that it has been elaborated and is 

 in advance, an improvement upon its ancestors. Only one naturalist 

 — Dr. Dijhrn, of Naples— has put forward * the hypothesis of dege- 

 neration as capable of wide ajiijlication to the explanation of existing 

 forms of life ; and his arguments in favour of a general application 



* ' Der Ursprung dor WirlxUliion' mid das Princip <U>8 Fmiclions-wjclisolH.' 

 (Lcip/iR, 187r).) 



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