ANATOMY OF MEDUSA 



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endoderm lining the cavity of the manubrium is thick, and 

 composed of columnar nutritive, and numerous gland-cells, 

 but it is reduced to a layer of simple cubical cells in the 

 radial and ring canals. The diagram shows a feature which 

 is of importance in enabling a comparison to be established 



Fig- S3- 



Development of the medusa In Podoeoryne carjtea^ a hydroid allied to 

 Obelia ; ec, ectoderm ; e?i^ endoderm ; dii, bell nucleus ; re, radial 

 canal ; cc, ring canal ; be, sub-umbreDar cavity ; w, manubrium ; el, 

 endoderm lamella ; i, tentacles ; v, velum, a circular curtain running 

 round the mouth of the bell, not developed in the medusa of Obelia; 

 07J, ova_ developing on the wall of the manubrium. For further 

 description of the figures see text. 



between the structure of a medusa and that of an ordinary 

 Hydroid polype. The section is represented as being slightly 

 oblique, so that on the left side of the picture it passes through 

 a radial canal, but on the right side it passes through the solid 

 substance of the umbrella. It can be seen that the mesogloea 

 is traversed by a thin sheet of solid endoderm continuous 



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