CHAPTEK 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 now more generally Arthropoda. Though 

 in these creatures the formation of segments may be inter- 

 preted as a disguised gemmation; and though, in some of 

 them, the number of segments increases by this modified bud- 

 ding after leaving the egg, as it does among the 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 differentiated one from another, at the same 

 time that they are severally more differentiated within them- 

 selves. Nor is there any instance of spontaneous fission 

 taking place in the series of segments composing an articu- 

 late 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 



* The name Annulosa, once used to embrace the Annelida and Arthro- 

 poda, has of late ceased to be used. It seems to me better than Appen- 

 diculaia, both as being more obviously descriptive and as being more 

 exclusive. 



Ill 



