92 THE POPULAR SCIENCE MONTHLY. 



of the organization of this primitive animal. If we assign to it the 

 organs still possessed by the segments of the Annelides, we find it to 

 have had an intestine separate from the circulation, being thus superior 

 to the polyps. It had also simple nervous and muscular systems, and 

 immature eyes, a chitinous armor, a water-vascular system, and possi- 

 bly distinct exterior breathing organs and feet. It may, indeed, have 

 been the primitive form from which other animal types besides the 

 Articulates originated through a diverse process of evolution. 



It is not improbable that the Articulate condition was reached, not 

 by a combination of free individuals, but by a continued adherence of 

 longitudinal buds. The increase in number of segments by division is 

 still common in Articulates. The minute fresh-water worm called 

 the Nais, is separated into two sections by a bud which appears in the 

 center of the body. One section develops a head and the other a tail, 

 at the ends adjoining the bud. But the bud itself again and again 

 divides, each division becoming a young Nais, so that finally a chain 

 of worms is formed, all organically connected, and fed by the mouth 

 of the anterior Nais. Eventually they sejDarate, each becoming a 

 free individual. 



The question now arises as to how a developing force would act 

 on such an articulated society. The highest results of evolution are 

 reached through concentration of function. Such specialization is op- 

 posed to a continuous increase in the number of segments, and must 

 tend to the production of a definite organism, of limited extent. The 

 activity of this organism is increased by its gaining limbs more useful 

 than the bristle-like setae of the Annelides. Its range of food expands 

 when its fore-limbs are changed into food-getting organs. Its powers 

 of motion increase when the body is compacted, and the number of 

 joints decreased, by a welding of several segments into one. 



But whence come such new limbs ? A consideration of their char- 

 acter leads us to the idea that they may proceed from a simple con- 

 tinuance of the budding process, acting, in this case, in a lateral direc- 

 tion instead of lengthwise. For the limbs are hollow, jointed seg- 

 ments, covered with chitine like the body-segments. They seem, in- 

 deed, to be specialized side-segments which have lost their internal 

 organs through disuse, retaining only their chitinous armor, their 

 muscles, and their intestinal cavity. And the successive joints of the 

 limbs appear to be formed by a continuance of the budding process. 

 One evidence of this is the fact that they may be reproduced by 

 budding when broken off at the joint ; and also that lateral budding 

 again takes place at the extremity of the limbs, yielding double tarsi 

 or pincers in the head-limbs. 



Such is the character of the articulated animal ; and it appears as 

 if this persistent partial individuality of the segments must prevent 

 that complete localization of function which seems necessary to the 

 greatest animal development'. 



