216 LEISURE-TIME STUDIES. 



The invariable law of heredity in the various examples 

 detailed is thus seen to operate sometimes in clear and 

 definite manner, converting the offspring into the likeness of 

 the parent directly, and with but little change, save that 

 involved 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 complicated process of development 

 and the observation of the manifold variations which the 

 working 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. 



Amongst the higher animals, as we have noted, the pro- 

 cess 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 of the body of the developing being con- 

 stitutes a process in which, from dissimilar or from simple 

 materials, the similarity of the animal 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 approxi- 

 mates to the parental type and likeness. Direct heredity 

 forms, in fact, the rule in higher life, just as indirect heredity 

 is a common feature of lower organisms. The frogs, toads, and 

 newts form the most familiar exceptions to this rule amongst 

 higher animals ; the young of these beings, as is well known, 

 appearing in the form of " tadpoles " (Fig. 8), and attain- 

 ing the likeness of the adult through a very gradual series 

 of changes and developments. But in no cases can the exist- 

 ence 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 

 diseases, are seen to be unerringly and exactly reproduced 

 through the operation of the law of likeness ; whilst in 

 certain unusual phases of development the influence of the 

 law can be shown not less clearly than in its common and 

 normal action. 



