210 TEE POPULAR SCIENCE MONTHLY. 



whose guiding pi-inciple is an unreasoning attachment to what is estab- 

 lished. Never, perhaps, was it shown more clearly than with reference 

 to the present question that innovation may be retrograde — that a pro- 

 posed change, if carried out, may involve a return to a lower stage of 

 development. What is the very essence of all advance to a higher 

 stage, of being, save differentiation ? We see what was at first homo- 

 geneous, uniform in structure, become resolved into distinct tissues and 

 members. We see functions which, in some rudimentary state, were 

 jointly exercised by the whole body of an animal, gradually allotted out 

 to special organs, and, during and in consequence of this very special- 

 ization, acquiring a far higher degree of perfection than they heretofore 

 possessed. Look at the first rudimentary state — germ, seed, or ovum — 

 of the plant or animal, and compare it with the mature organism to 

 which it ultimately gives rise. What was one has become manifold ; 

 what was simple is now highly complex. The globule of albuminoid 

 matter has developed into distinct members — sense-apparatus, organs 

 respiratory, digestive, circulatory, locomotive, etc. — each of which has 

 a separate task to fulfill, and is distinctly organized for that very pur- 

 pose. It is no departure from our subject to remark that, though in 

 the organic body one organ may, under certain circumstances, undertake 

 the duties of another, such vicarious action involves grave peril to the 

 organ concerned, and to the entire animal. Perhaps the world may yet 

 find that the analogy between the individual and mankind holds good 

 in this respect, and that a social congestion may follow from the move- 

 ment we are examining. 



To return : the increase of size which distinguishes the butterfly 

 from the Qg^^ or the oak from the acorn, is a trifling feature compared 

 with the accompanying diff'erentiation— chemical, morphological, and 

 functional — which has taken place. 



If we pass from a consideration of the individual plant or animal to 

 a survey of the entire organic realms, we find, as we advance from the 

 humblest and meanest beings to the highest, merely a repetition of the 

 same great fact. At the one extremity of the scale — if this expression 

 may still be used — we find beings whose senses, such as they are, must 

 be exercised by the whole external surface of the body, those more 

 special functions which we know as sight, hearing, etc., being still 

 identical with feeling. No distinct nervous system, still less definite 

 nerve-centres, can be traced. Nor are there any organs specially de- 

 voted to the processes of respiration, circulation, digestion, etc. A 

 common internal cavity takes the place, and, in a crude way, fulfills the 

 duties of all these parts. Externally the same uniformity prevails ; 

 there are no limbs, no members exclusively constructed for locomotion 

 in any of its modes, or for prehension. The animal moves by elongating 

 and contracting its whole body, or by rolling over. In many of the 

 lower forms of animal life the sexes are not separated, the functions of 

 the male and the female being exercised by one and the same individual. 



