No. 4.] MORPHOLOGY OF Till-: ACTI. \OZOA. 157 



endocoelic spaces bounded by the perfect mesenteries. The 

 sections did not, unfortunately, cut the column perfectly trans- 

 versely, but the arrangement which obtained may be perceived 

 from the representation of the half of one section shown in Fig. i , 

 and from the diagram (Fig. 2) which represents a reconstruction 

 from a perfect series of sections. On each side of the median 

 line of Fig. i is one of a pair of directives, that to the right 

 being cut at the level of the oral stoma, as is also another 

 mesentery in the right half of the figure. On each side of the 



T 



FIG. i. Transverse section through the upper part of the column of Halcurias pilatjis. 

 T = tentacle . D directive mesenteries . 



directives is a perfect mesentery with its muscle pennon on 

 the same side as that of the adjacent directive, and on the left 

 side this mesentery is succeeded by one which evidently forms 

 with it a typical pair, though it may be noticed that the endo- 

 coel enclosed by this pair is broader than the adjacent exocoels. 

 On the right side, where, owing to the obliquity of the sec- 

 tions, the column is cut higher up, the bases of some of the 

 tentacles (T) being cut, the mesenteries of the first lateral pair 

 are widely separated, and between them three imperfect pairs 

 occur, which evidently represent two cycles. The succeeding 



