PLAT XVII. 



ISOPHYLLIA DIPSACEA Dana. 



Fig. 121. — Vertical section through the overfolded part of the column wall of a retracted polyp, showing the sphincter 



muscle supported on somewhat complicated mesogloeal foldings. X 200. 

 Fig. 122. — Vertical section through a part of the column wall. Dark granular matter occurs in restricted patches 



within the ectoderm. X 220. 

 Fig. 123. — Free portion of a mesentery terminated by a mesenterial filament. The musculature is here very feeble, 



and the mesogloea is narrow and smooth on both faces. X 300. 

 Fig. 124. — Isolated nematocysts; o, from tentacular ectoderm; h, from mesenterial filaments, x 900. 

 Fig. 125. — Larva shortly after extrusion. The wall is partly transparent, and shows three pairs of mesenteries; one 



strongly developed pair extends practically the full length of the larva, while the two others extend but 



a short distance. Enlarged. 

 Fig. 126. — Transverse section through the uppermost stomodreal region of a freshly extruded larva. Two pairs of 



mesenteries with thickened mesogloea extend from the column wall to the stomodseum, but the ventral 



pair (III, III) is free. X 200. 

 632 



