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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



development into the similitude of the being 

 which gave it birth. So accustomed are we to 

 trace this direct resemblance between the parent 

 and the young in the higher animals and among 

 ourselves, that any infringement of the law of 

 likeness is accounted a phenomenon of unusual 

 kind. Even extending to the domain of mind as 

 well as of body, we unconsciously expect the child 

 to exhibit the traits of character and disposition 

 which are visible in its parents, and to grow up 

 " the child of its father and mother," as the ex- 

 pression runs, in every phase of its bodily and 

 mental life. 



A wider view of the relations and harmonies 

 existing in Nature, however, shows us that this 

 direct development of the young into the simili- 

 tude of its ancestors is by no means of universal 

 occurrence. Many forms attain the resemblance 

 to their progenitors only after passing through a 

 series of changes or disguises, often of very com- 

 plicated nature. And a very slight acquaintance 

 with the facts of physiology would serve to show 

 that the law of likeness, like most other laws 

 regulating the world of life, has its grave excep- 

 tions, and that it exhibits certain phases of sin- 

 gular interest in what may be termed its abnor- 

 mal operation. The young of an animal or plant 

 may, and frequently do, exhibit very remarkable 

 variations from tbe parent in all the characteris- 

 tics which are associated with the special nature 

 of the being. The circle of repeated and perpetu- 

 ated likeness may thus be broken in upon at any 

 point, and the normal law of heredity may be re- 

 garded as occasionally superseded in its working 

 by the operation of another law — that of varia- 

 tion and divergence. Forms unlike the parents 

 are thus -known to be frequently produced, and 

 these errant members of the family circle may be 

 shown to possess no inconsiderable influence on 

 the nature and constitution of the world of life 

 at large. Family likeness, as every one knows, 

 lies at the root at once of the differences between, 

 and relationships of, living beings. The offspring 

 must resemble their parents and their own kind 

 more closely than they resemble other groups, 

 else our knowledge of the relationship of one 

 form to another must be regarded as possessing 

 no sound basis whatever. But admit that the 

 young may not resemble the parent, and a veri- 

 table apple of discord is at once projected into 

 the apparent harmonies of Nature, and dire con- 

 fusion becomes the order of the day. As will 

 be hereafter shown, however, while the law of 

 variation does undoubtedly operate, and that to a 

 very great extent, among living beings, other and 



compensating conditions are brought to light by 

 the careful study of development at large ; and 

 the old law of like producing like may be seen, 

 after all, to constitute the guiding principle of 

 Nature at large. As a study of high interest, and 

 one the elements of which are afforded by our ob- 

 servation of the every-day world, the investigation 

 of the law of likeness may be safely commended 

 to the seeking mind. And in the brief study of 

 this law and its operations we may firstly glance 

 at some instances of development by way of 

 illustration, and thereafter try to discern the 

 meaning and causes of similitude or heredity. 

 " Rassemblons des fails pour nous donner des 

 idees" says Buffon, and the advice is emi- 

 nently appropriate to those who purpose to 

 enter upon a popular study of an important 

 natural law. 



One of the simplest instances of development, 

 in which the young are not only transformed di- 

 rectly into the likeness of the parent, but repre- 

 sent in themselves essential parts of the parent- 

 body, is illustrated by the case of the little worms 

 known to the naturalist as Naidides, and familiar 

 to all as inhabitants of our ditches, and as occur- 

 ring in damp mud and similar situations. If a 

 Na'is be chopped into a number of small pieces, 

 each piece will in time develop a head and tail 

 and become a perfect worm, differing in no re- 

 spect, save in that of size, from the original form. 

 A Na'is cut into forty pieces was transformed 

 through the operation into as many small worms 

 of its own kind. Here the law of likeness or he- 

 redity operates in the plainest and most direct 

 fashion. The young aie like the parent-stock, 

 because they consist in reality of detached por- 

 tions of the parent's personality. The experi- 

 ments of naturalists carried out on animals of 

 lower organization than these worms, such as 

 the little fresh-water polyp or hydra, show a pow- 

 er of artificial reproduction which is of literally 

 marvelous extent; and all such animals eviuce at 

 onee the simplest mode of development and the 

 plainest reasons why the young should exactly re- 

 semble the parent. It might, however, be alleged 

 that such artificial experimentation was hardly 

 to be accepted as illustrative of natural develop- 

 ment ; but in answer to such an observation the 

 naturalist might show that an exactly similar 

 method of reproduction occurs spontaneously 

 and naturally in the Na'is and in certain other 

 animals of its class. A single Na'is has been ob- 

 served to consist of four connected but distinct 

 portions, the hinder three of which had become 

 almost completely separated from the original 



