Plate VIII. Fig. 15. Sections showing the relations of ectoderm (EC), 

 endoderm (EN) and mesoglea (M). The endoderm cells have muscle filaments 

 in their base and send processes into the mesoglea. If the origin of the 

 processes is missed in section, the processes appear to be lying as organelles 

 or inclusions in the mesoglea. The mesoglea has no membrane around it. If 

 the cell membranes of adjacent cells are traced for a short distance from the 

 mesoglea, collections of granules, similar to those in the mesoglea, can be 

 found in the extracellular space (arrow). 



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