PLAT XVII. 



ISOPHYLLIA DIPSACEA Dana. 



Fici. 121. — Vertical section through the overfolded part of the column wall of a retracted jiolyp, nli<i\vin.ir the n]ihincter 



muscle supported on somewhat complicated mesogiO*al foldings. X 200. 

 Fid. 122. — Vertical section through a part of the column wall. Dark granular matter occur.s in restricted ))atches 



witliin the ectoderm. X 220. 

 F[i;. 123. — Free portion of a mesentery terminated by a mesenterial lilament. Tlie musculature is here very feeble, 



and the mesogl(ca is narrow and smooth on liotli faces. X 300. 

 Fiii. 124. — Isolated nematocysts; a, from tentacular ectoderm; h, from mesenterial filaments. X 900. 

 Fi(i. 125. — Larva shortly after extrusion. The wall is partly trans] larent, 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, 

 l'"!!;. 126. — Transverse section through the uppermost stomodreal region of a freshly e.xtruded larva. Two pairs of 



mesenteries with thickened mesogln^a extend from the column wall to the stomodreum, but the ventral 



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

 632 



