THE ANIMAL KINGDOM 



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segmented. Thirdly, a characteristic development has 

 occurred in the mesoderm or middle body-layer of 

 these animals. In the phyla so far considered there 



Fig. 3. Transverse section through an Annelid, al. alimentary 

 canal, end. endoderm. ect. ectoderm, coel. perivisceral coelom. 

 c.ep. coelomic epithelium applied to body wall (somatopleur). 

 c.ep'. coelomic epithelium applied to gut (splanchnopleur). 

 5. blood-vessels, n. ventral nerve-cord, neph. nephridium. st. 

 coelomostome or gonadial funnel, g. gonad. mus.c. circular 

 muscles, mus.l. longitudinal muscles. 



has been no formation of definite cavities or spaces 

 in this body-layer, no differentiation of blood-vessels 

 from a body-cavity ; but in the Appendiculata a 

 spacious cavity is developed in the mesoblast lined 



