THE LA W OF LIKENESS, AND ITS WORKING. 



555 



each egg directly develops. And similarly with 

 the salpse. The chain-salpa may be regarded as 

 corresponding to the zoophyte, each individual 

 of the chain producing an egg, which develops 

 again into a chain-salpa, through the medium of 

 the single and unconnected form. 



To a still greater extent in insects and some 

 crustaceans — such as barnacles, etc. — may the 

 process of development be complicated and ex- 

 tended. The egg of the butterfly gives origin, 

 not to the aerial winged insect, but to the mun- 

 dane caterpillar, which, after passing an existence 

 devoted solely to the work of nourishing its body, 

 envelops that body in a cocoon and becomes the 

 chrysalis ; finally appearing from this latter in- 

 vestment as the winged and mature form. In 

 the case of all insects which, like the butterfly, 

 pass through a metamorphosis, as the series of 

 changes is named, the law of likeness appears to 

 be protracted, and its terms somewhat evaded or 

 extended. The egg, in other words, develops 

 into the mature form only after passing through 

 an extended development, and evolves the simili- 

 tude of the parent-form through certain interme- 

 diate stages of well-marked kind. And so, also, 

 with the well-known barnacles which attach them- 

 selves to the sides of the ships and to floating 

 timber. The young barnacle appears as an ac- 

 tive little creature, possessing limbs adapted for 

 swimming, along with feelers, eyes, and other 

 appendages. Ultimately, the embryo barnacle 

 forms its shell, loses its limbs and eyes, attaches 

 itself by its feelers to some fixed object, develops 

 its flexible stalk, and passes the remainder of its 

 existence in a fixed and rooted condition. The 

 development in this latter case, although in due 

 time producing the likeness of the parent, clearly 

 leads to a state of life of much lower character, 

 and to a structure of humbler grade, compared 

 with the life and organization of the young bar- 

 nacle. The invariable law of heredity in the va- 

 rious examples detailed is thus seen to operate 

 sometimes in clear and definite manner, convert- 

 ing the offspring into the likeness of the parent 

 directly, and with but little change, save that in- 

 volved in the process of growth, into the parent- 

 form. In other cases, the operation of the law is 

 carried out through an extended and often com- 

 plicated process of development ; and the obser- 

 vation of the manifold variations which the work- 

 ing of the law exhibits, adds but another to the 

 many proofs of the inherent plasticity of Nature, 

 and the singular adaptations which are exhibited 

 to the varying necessities of living beings. 



Among the higher animals, as we have noted, 



the process of development for the most part 

 evolves the likeness of the parent in a simple 

 and direct manner. True, in all higher animals, 

 as in lower animals, the mere formation of organs 

 and parts in the body of the developing being 

 constitutes a process in which, from dissimilar or 

 from simple materials, the similarity of the ani- 

 mal to its parent and to the intricacy of the adult 

 form are gradually evolved. But we miss in 

 higher animals these well-defined and visible 

 changes of form through which the young being 

 gradually approximates to the parental type and 

 likeness. Direct heredity forms, in fact, the rule 

 in higher life, just as indirect heredity is a com- 

 mon feature of lower organisms. The frogs, 

 toads, and newts, form the most familiar excep- 

 tions to this rule among higher animals ; the 

 young of these forms, as is well known, appearing 

 in the form of " tadpoles," and attaining the like- 

 ness of the adult through a very gradual series 

 of changes and developments. But in no cases 

 can the existence of hereditary influences be more 

 clearly perceived or traced than in cases of the 

 development of higher animals, in which traits 

 of character, physical peculiarities, and even dis- 

 eases, are seen to be unerringly and exactly re- 

 produced through the operation of the law of 

 likeness ; while in certain unusual phases of de- 

 velopment the influence of the law can be shown 

 not less clearly than in its common and normal 

 action. 



The case of the " ancon " or " otter " sheep 

 serves as an apt illustration, not only of the trans- 

 mission of characters to the offspring, but like- 

 wise of the sudden appearance and development 

 of characters not accounted for by heredity. In 

 the year 1791 a ewe belonging to a Massachusetts 

 farmer produced a lamb differing materially from 

 its neighbors in that its legs were disproportion- 

 ately short, while its body was disproportionately 

 long. This departure from the ordinary type of 

 the sheep could not be accounted for in any way ; 

 the variation being, as far as could be ascertained, 

 perfectly spontaneous. The single short-legged 

 sheep became the progenitor of others, and in 

 due time a race of ancons was produced ; the va- 

 riety, however, falling into neglect, and ultimately 

 disappearing, on account of the introduction of 

 the Merino sheep, and of the attention paid to the 

 development of the latter breed. The law of like- 

 ness in the case of the ancon sheep proved nor- 

 mal in its working after the introduction of the 

 first ancon. The offspring of two ancons was 

 thus invariably a pure otter sheep ; the progeny 

 of an ancon and an ordinary sheep being also 



