THE METAMORPHOSIS. 435 



from a, in every respect, general form to one more particular and deter- 

 minate. This character displays itself most distinctly in the perfect 

 insect in the separation of the entire body into three particular divi- 

 sions, each of which comprises its peculiar organs. It likewise stands 

 in the closest connexion with the general ideas of development, and of 

 the higher perfection of organic natural bodies, in as far as by this 

 structure of the body the individual organs are more distinctly separated 

 from each other, and each has acquired its determinate situation and a 

 more artificial composition. The head is the bearer of the organs of 

 the senses, the thorax of those of motion, and in the abdomen the 

 organs of vegetation are placed. That portion of the body, conse- 

 quently, which in the series of Gastrozoa predominated has become in 

 the insect if not the smallest yet the most simple and least developed, 

 whereas that in which all the organs are situated that characterise the 

 Arthrozoa, which are the organs of motion, namely, the thorax, is, with 

 respect to its composition and development, the most perfect. But we 

 have above seen ( 158) that the organs of motion fall into active and 

 passive. But this separation is first found distinctly expressed in the 

 Arthrozoa. We certainly find the active ones or muscles universally 

 among the Gastrozoa, and also indications of the passive ones are found 

 in the internal bony parts and partial skeleton ; but a perfect skeleton 

 of hard parts to which the muscles can be attached is first found in the 

 higher Arthrozoa, namely, the Crustacea and Iiisecta, and which 

 presents itself as an external ossified or horny integument. The most 

 simple form of this external integument is the ring, all particularities 

 and individual divarications have consequently proceeded from the 

 annular form, and must, therefore, admit of being referred back again 

 to it. The first change, however, which the ring in the progress of deve- 

 lopment suffers is, that it separates into a superior and inferior half; 

 thus are formed the rings or segments of the abdomen, as well as of 

 many larvae and caterpillars. Whence the lower half thickens in its 

 centre, and from this spot sends processes inwardly, which also occa- 

 sionally form into a ring, and thus a smaller ring is inclosed within 

 the larger one, but both of which touch at one spot, namely, where a 

 half diameter drawn from the centre touches the circumference. This 

 inner ring, or the processes which indicate it, receive the nervous cord 

 within it, whereas all the other organs are encompassed by the larger 

 external ring. Thus are formed the most perfect segments, namely, 

 those of the thorax. 



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