26 HYUEA. 



2. The mesoglcea is seen in transverse sections as a very 



thin transparent layer, between the ectoderm and 

 the endoderm. 



3. The endoderm cells differ greatly in shape in different 



parts of the body and at different times. During 

 life they are amoeboid, and their processes may 

 extend so far as to almost obliterate the cavity of the 

 animal. They contain vacuoles, which are often so 

 large that the cell-substance is reduced to a thin 

 peripheral lamella. The nucleus is usually nearer 

 the outer or basal end, and is flattened in shape. 

 The flagella can very seldom be seen in sections. 



In the foot the endoderm cells are much smaller 

 than in the body, and form a layer of short columnar 

 or almost cubical cells containing granular concre- 

 tions. 



