CHAPTER V. 



THE MORPHOLOGICAL COMPOSITION OF ANIMALS, 

 CONTINUED. 



208. INSECTS, Arachnids, Crustaceans, and Myriapods, 

 are all members of that higher division of the Annulosa called 

 Articulata or Arthropoda. Though in these creatures the 

 formation of segments may be interpreted as a disguised 

 gemmation ; and though in some of them the number of seg- 

 ments increases by this modified budding after leaving the 

 egg, as among the higher Annelids ; yet the process is not 

 nearly so dominant : the segments are usually much less 

 numerous than we find them in the types last considered. 

 In most cases, too, the segments are in a greater degree dif- 

 ferentiated one from another, at the same time that they 

 are severally more differentiated within themselves. Nor is 

 there any instance of spontaneous fission taking place in the 

 series of segments composing an articulate animal. On the 

 contrary, the integration, always great enough permanently 

 to unite the segments, is frequently carried so far as to hide 

 very completely the individualities of some or many of them ; 

 and occasionally, as among the Acari, the consolidation, or 

 the arrest of segmentation, is so decided as to leave scarcely 

 a trace of the articulate structure : the type being in these 

 cases indicated chiefly by the presence of those character- 

 istically-formed limbs, which give the alternative name 

 Arthropoda to all the higher Annulosa. Omitting the para- 

 sitic orders, which, as in other cases, are aberrant members of 



