386 



TORREY 



have a thick ectoderm with the customary masses of nematocysts and 

 layer of deeply lying nervous tissue. The mesoglcea is thick. The 

 endoderm is lower, with few gland cells and a layer of circular muscle 

 fibers. 



There is no special sphincter muscle. The endodermal circular 

 muscles are strongly developed throughout the column. The ectoderm 

 of the oesophagus contains numerous deeply staining gland cells with 

 distinctly granular contents, thus differing from the homogeneous cells 

 in a similar position in Charisea. There is but one siphonoglyph, 

 placed in a position corresponding to one end of the mouth. 



There are twelve pairs of mesenteries, each with a parietal ostium. 

 They may best be discussed in connection with the accompanying 

 diagram (fig. i6). The latter represents the body wall and oesopha- 

 gus as having been sectioned longitudinally on one side between one 

 pair of directives, and then stretched out flat so that the relations of the 

 mesenteries might be more readily seen. The narrow horizontal lines 

 at the top of the figure indicate the limits of the oesophagus, which is 



represented as transparent, though 

 not actually so. The narrow ver 

 tical lines represent the mesenteries, 

 the length of these lines suggest- 

 ing, not the length of the mesen- 

 teries, all of which are continued to 

 the extremity of the body, but their 

 relative importance in width and 

 in size of retractors. The heavy 

 lines on all of the mesenteries rep- 

 resent the mesenterial filaments, 

 each a single strand of epithelium 

 crowded with gland cells and resting 

 on a cushion of epithelium. There 

 are no acontia. The broad black 

 bands represent gonads (fig. 17.) 



It is evident at once that the mes- 

 enteries are arranged on a hexam- 

 erous plan in two alternating cycles 

 which differ in several respects. 

 The mesenteries of the second cycle 

 are smaller than those of the first, 

 their retractor muscles are not so strong, and they may only occasion- 

 ally bear gonads. The filaments on all the mesenteries begin at the 



Fig. 17. Harenactis attentiata. 

 Cross section o£ primary mesentery 

 through mesenterial filament, 

 gonad and longitudinal muscle. 



