in. ANNELIDA. 



305 



Class III. Annelida. 



The segmentation of the body, which was shown in a slight de- 

 reaclies its highest develgpment in the 



a'lX'o in the C'hajtocrnatlii, 



Fig. 27:3.— Diagram of annelid somites (orig.). tn/i, acieular mu.scles: o, ca^lom;cm, 

 circular muscles ; cv, circular blood-vessels; d, dorsal blood-vessel; (, intestine ; 

 ItH^ longitudinal muscles: m. mesentery; ii. nerve cord; j(«, nephridium; 7ie, ?tv, 

 neuro- and notopodia, forming parapodium; s, septum; so, somatopleure; sp, 

 splanchnopleure; f, typhlosote. 



Annelids, where it api^ears both in the outer ringing of the body 

 and in the arrangement of the most important systems of organs — 

 mctameric arrangement of excretory organs, nervous system, blood- 



De.ZJH, 



vessels — internal segmentation. To this is added an extraordinary 

 increase in number of body segments (somites, metameres), which 

 can far exceed a hundred. AVe can thus define the Annelids as 



