252 



NATURE 



{Jan. 25, 1872 



THE LAWS Of ORGANIC DEVELOPMENT* 

 'T'HE discussion of this subject divides itself into two parts, 

 ■*■ viz. : a consideration of the proof that evolution of organic 

 types, or descent with modificatiO'>, has taken place ; and, 

 secondly, the investiga'ion of the laws in accordance with which 

 this development has progressed. 



L— Ok the Proof for Evolution. 



There are two modes of demonstration, both depending on 

 direct observation. One of these has been successfully presented 

 by Darwin. He has observed the origin of varieties in animals 

 and plants, either in the domesticated or wild states, and has 

 shown, what had been known to many, the lack of distinction 

 in the grades of difference which separate varieties and species. 

 But he has also pointed out that species {such, so far as distinct- 

 ness goes) have been derived from other species among domes- 

 ticated animals, and he infers by induction that other species, 

 whose origin has not been observed, have also descended from 

 common parents. So far 1 believe his mduction to be justified : 

 but when from this basis evolution of divisions defined by im- 

 portant structural characters, as genera, orders, classes, &c., is 

 mferred, I believe that we do not know enough of the uniformity 

 of nature's processes in the premises to enable us so regard this 

 kind of proof as conclusive. 



I therefore appeal to another mode of proving it, and one 

 which covers the case of all the more really structural features of 

 .inimals and plants. 



It is well known that in both kingdoms, in a general way, the 

 young stages of the more perfect types are represented or imitated 

 with more or less exactitude by the adults of inferior ones. But 

 a tiue identity of these adults with the various stages of the 

 higher has, comparatively, rarely been observed. Let such a 

 case be supposed. 



In A we have four species whose growth attains a given point, 

 a certain number of stages having been passed prior to its termi- 

 nation or maturity. In B we have another series of four (the 

 numbering a matter of no importance), which, during the period 

 of growth, cannot Le distinguished by any common, i.e.^ generic 

 character, from the individuals of group A, but whose growth 

 has only attained to a puint short of that reached by those of 

 group A at maturity. Here we have a parallelism, but no true 

 evidence of descent. Bat if we now find a set of individuals 

 belonging to one species, and therefore held to have had a 

 common origin or parentage (or still bttter the individuals of a 

 single brood), which present differences among themselves of the 

 character in question, we have gained a point. We know in this 

 case that the individuals a, have attained to the completeness of 

 character presented by group A, while others, h, of the same 

 parentage, have only attamed to the structure of those of group 

 B. It is i^erfectly obvious that the individuals of the first ]')art 

 of the family have grown further, and, therefore, in one sense 

 faster, than those of group h. If the parents were like the 

 individuals of the more completely grown, the o.ffspring which did 

 not attain that completeness may be said to have been retarded 

 in their development. If, on the other hand, the parents were 

 like those less fully grown, then the offspring which have added 

 something have been aecelerateit m their deve'opment. 



I claim that a consideration of the uniformity of nature's pro- 

 cesses, or inductive reasoning, requires me (however it may affrct 

 the minds of others) to believe that the groups of species whose 

 individuals I have never found to vary, but which differ in the 

 same point as those in which I have observed the above varia- 

 tions, are also derived from comm -n parents, and the more ad- 

 vanced have been accelerated or the less advanced retarded, as 

 the case may have been with regard to the parents. 



This is not an imaginary case, but a true representation of many 

 which have come under my observation. I'he developmental 

 resemblances mentioned are universal in the animal and probably 

 in the vegetable kingdoms, approaching the exactitude above 

 depicted in proportion to the near structural similarity of the 

 species considered. 



II. — Oil the Puzi's of Evoliitiofi. 



Wallace and D.irwin have propounded as the cause of modifi- 

 cation in descc' t their law o( natunl selection. This lai- has 

 beeti epi omsed by .Spencer a 'he "preservation of the fittest." 

 This neat expre-sion no d' ubt covers the case, but it leaves the 



* Abstract or paper by Pror. E. D. Cope, read at the Indianaiolis meetni^- 

 cf tile American A^^ociation for the Advancement of Science : reprinted 

 fiom tlic American Naturcttiat. 



origin of the fittest entirely untouched. Darwin assu.nes a 

 " tendency to variation " in nature, and it is plainly necessary to 

 do this in order that materials for the exercise of a selection 

 sh uld exist. Darwin and Wallace's law is, then, only restrictive, 

 directive, conservative, or destructive of something already created. 

 Let u<:, then, seek for the originative laws by which these subjects 

 are furnished— in other words, for the causes of the origin of the 

 fittest. 



The origin of new- structures which distinguish one generation 

 from those which have preceded it, I have stated to take place 

 under the law of acceleration. As growth (creation) of paits 

 usually ceases with maturity, it is entirely plain that the process 

 of acceleration is limited to the period of infancy and youth in 

 all animals. It is also plain that the question of growth is one 

 of nutrition, or of the construction of organs and tissues out of 

 protoplasm. 



The construction of the animal types is restricted to two kinds 

 of increase — the addition of identical segments and the addition 

 of identical c-Ils. The first is probably to be referred to the last, 

 but the laws which give rise to it cannot be here explained. Cer- 

 tain it is that segmentation is not only produced by addition of 

 identical parts, but a'so by subdivision of a homogeneous part. 

 In reducing the vertebrate or most complex animal to its simplest 

 expression, we find that all its specialised parts are but modifica- 

 tions of the segment, either simply or as sub-segments of com- 

 pound but identical segments. Gegenbaur has pointed out that 

 the most complex limb with hand ( r foot is constructed, fir>t, of 

 a single longitudinal series of identical segments, from each of 

 which a similar segment diverges, the whole forming parallel 

 series, not only in the oblique transverse, but generally in the 

 longitudinal sense. Thus the limb of the Lepidosiren represents 

 the simple type, that of the Ichthyosaurus a first modification. 

 In the latter the first segment only (femur or humerus) is S| eci- 

 alised, the other pieces being undistinguishable. In the Plcsio- 

 saurian paddle the separate parts are distinguished ; the ulna and 

 radius well marked, the carpal pieces hexagonal, the phalanges 

 well marked, &c. 



As regards the whole skeleton, the same position may be 

 safely assumed. Though Huxley may reject Owen's theory of 

 the verlebrate character of the segments of the cranium, because 

 they are so very different from the segments in other paits of 

 the column, the question rests entirely on the definition of a 

 vertebra. If a vertebra be a segment of the skeleton, of course 

 the skull is composed of vertebna? j if not, then the cranium may 

 be said to be lormed of " sclerotomes," or some other name may 

 be used. Certain it is, however, that the parts of the segments 

 of the cranium may be now more or less completely parallelised 

 or homologised with each other, and that as we descend the 

 scale of vertebrated animals, the resemblance of these segments 

 to vertebra" increases, and the constituent segments of each become 

 more similar. In the types where the greatest resemblance is 

 seen, segmentation of either is incomplete, fL>r they retain the 

 original cartilaginous basis. Other animals which present cavi- 

 ties or parts of a solid support are still more easily reduced to a 

 simple basis of segments, arranged either longitudinally (worm) 

 or centrifugally (star-fish, &c. ). 



Each segment — and this term includes not only the parts of a 

 complex whole, but parts always subdivided, as the jaw of a whale 

 or the sac-body of a mollusc — is constructed, as is well known, by 

 cell-division. In the growing ffetus the first cell divides its 

 nucleus and then its whole outline, and this process repeated 

 millions of times produces, according to the cell theory, all the 

 tissues of the animal organism or their bases from first to last. 

 That the ultimata or histological elements of all organs are pro- 

 duced originally by repetitive growth of simple, nucleated cells 

 with various modifications of exactitude of repetition in the more 

 complex, is taught by the cell theory. The formation of some 

 of the tissues is as follows : — 



First Chnnge — Formation of simple nucleated cells from homo- 

 geneous protoplasm or the cytoblastema. 



Second — Formation of new cells by division of body and nucleus 

 of the o'd 



Third — Formation of tissues by accumulation of cells with 

 or without addition of intercellular cytoblastema. 



A. In connective tis-ue by slight alteration of cells and addi- 

 tion of cvohlastena. 



B. In ijl'io-i, by addi ion of fluid cytcablaste-na (fibrin) to free 

 cells (lymph cor.u-clcs), which in higher animals (vcr clirates) 

 develop into lilood-corpuscles by loss of membrane, and by cell 

 development of muscles. 



