FREE BOOKS

Author's List




PREV.   NEXT  
|<   86   87   88   89   90   91   92   93   94   95   96   97   98   99   100   101   102   103   104   105   106   107   108   109   110  
111   112   113   114   115   116   117   118   119   120   121   122   123   124   125   126   127   128   129   130   131   132   133   134   135   >>   >|  
inged Insects, with head, chest, and hind body distinct from each other, forming three separate regions. In the first group, the Centipedes, the nervous system is scattered through the whole body, as in the Worms; in the Spiders it is concentrated in two nervous swellings, as in the Crustacea, the front one being the largest; and in the Insects there are three nervous centres, the largest in the head, a smaller one in the chest, and the smallest in the hind body. Now according to this greater or less individualization of parts, with the corresponding localization of the nervous centres, naturalists have established the relative rank of these three groups, placing Centipedes lowest, Spiders next, and Winged Insects highest. But naturalists may, and indeed they actually do, differ as to this estimation of the anatomical structure. Have we, then, any means of testing its truth to Nature? Let us look at the development of these animals, taking the highest order as an illustration, that we may have the whole succession of changes. All know the story of the Butterfly with its three lives, as Caterpillar, Chrysalis, and Winged Insect. I speak of its three lives, but we must not forget that they make after all but one life, and that the Caterpillar is as truly the same being with the future Butterfly as the child is the same being with the future man. The old significance of the word _metamorphosis_--the fabled transformation of one individual into another, in which so much of the imagination and poetical culture of the ancients found expression--still clings to us; and where the different phases of the same life assume such different external forms, we are apt to overlook the fact that it is one single continuous life. To a naturalist, metamorphosis is simply growth; and in that sense the different stages of development in animals that undergo their successive changes within the egg are as much metamorphoses as the successive phases of life in those animals that complete their development after they are hatched. But to return to our Butterfly. In its most imperfect, earliest condition, it is Worm-like, the body consisting of thirteen uniform rings; but when it has completed this stage of its existence, it passes into the Chrysalis state, during which the body has two regions, the front rings being soldered together to form the head and chest, while the hind joints remain distinct; and it is only when it bursts from its Chrysa
PREV.   NEXT  
|<   86   87   88   89   90   91   92   93   94   95   96   97   98   99   100   101   102   103   104   105   106   107   108   109   110  
111   112   113   114   115   116   117   118   119   120   121   122   123   124   125   126   127   128   129   130   131   132   133   134   135   >>   >|  



Top keywords:

nervous

 

Insects

 

Butterfly

 
development
 
animals
 

successive

 
naturalists
 

Chrysalis

 

Caterpillar

 

distinct


metamorphosis
 

Winged

 

highest

 

phases

 

Centipedes

 
future
 

regions

 

Spiders

 

centres

 
largest

individual

 
external
 

overlook

 

fabled

 

ancients

 

transformation

 

poetical

 
clings
 

assume

 

imagination


expression

 

culture

 

metamorphoses

 

existence

 

passes

 

completed

 

uniform

 

consisting

 

thirteen

 

soldered


bursts

 

Chrysa

 

remain

 

joints

 

condition

 

stages

 
undergo
 

growth

 

simply

 

continuous