THE WONDERS OF LIFE 



the articulates and vertebrates rise above all the other 

 metazoa by the perfection of their organism and the 

 variety of their functions. In the articulates the meta- 

 merism is chiefly external — an articulation of the body 

 wall. In the vertebrates it mainly affects the internal 

 organs, the skeleton, and the muscular system. The 

 vertebration (articulation) of the vertebrates is not out- 

 wardly visible like that of the articulates. In both stems 

 the articulation is similar in the lower and upper forms, 

 as we find in the annelids and myriapods, the acrania and 

 cyclostoma. On the other hand, the higher the organi- 

 zation the greater is the unlikeness of the members or 

 articulated parts, as in the arachnida and insects, the 

 amphibia and amniotes. The same antithesis is found 

 in the lower and higher Crustacea. This metamerism 

 of the higher metazoa is of a motor character, having 

 been acquired through the manner of movement of the 

 lengthened body; but we find in some groups of the 

 lower, and usually unarticulated, metazoa a propagative 

 metamerism, determined by budding at the end; such is 

 the strobilation of the chain-worms and the scyphostoma 

 polyps. The individual metamera (parts) that are 

 released from the end of the chain in these cases im- 

 mediately show their individuality. This is also the 

 case with many of the annelids, in which every member 

 that is separated has the power to reproduce the whole 

 chain of metamera. 



The third and highest stage of individuality to which 

 the multicellular organism attains is the stock or colony 

 {cormiis). It is usually formed by a permanent associa- 

 tion of histonals that are produced by cleavage (imper- 

 fect segmentation or budding) from one histonal indi- 

 vidual. The great majority of the metaphyta form 

 complex plants in this sense. But among the metazoa 

 we find this form of individuality only in the lower (and 

 generally stationary) stages of development. Here also 



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