No. 2.] MORPHOLOGY OF THE ACTINOZOA. 1 39 



somewhat bilobed, constricted by a well-marked " neck," and 

 evidently comparable with the " Flimmerstrcifen " of the mes- 

 enterial filaments of the Hexactiniae. The section has not cut 

 all the mesenteries at the same relative level, so that those 

 furthest from the ventral median line show features which are 

 to be found in i, 4, and 3, a little farther down. The mesentery 

 (4') which succeeds 3 is again of the fourth grade. It is much 

 wider than those nearer the middle line, and its mesenterial 

 filament is quite different, appearing simply as a small rounded 

 knob at the free edge of the mesentery not separated dis- 

 tinctly from the endoderm by a neck, and corresponding to the 

 " Nesseldriisenstreif " of the Hexactiniae. A few sections 

 higher up this mesentery, and the other mesenteries of the 

 fourth grade represented (4" and 4'"), which resemble it in 

 width and structure, are exactly similar in all points to 4. The 

 three mesenteries which alternate with 4', 4", and 4'" are of 

 the second (2), third (3'), and first (i') grades, and exactly 

 resemble i. 



Figure 4 is a section nearly 2 mm. below that just described. 

 The ventral directives, only one of which is figured {D), have 

 practically disappeared, being indicated simply by a slight 

 elevation of the mesogloea. The mesenteries of the first, third, 

 and second grades nearest the middle line (i, 3, and 2) are 

 broader than they were higher up, but still retain the same kind 

 of filaments they possessed there. The more external (dorsal) 

 mesenteries are much wider, and, in fact, have now reached 

 their final width, and ova have begun to appear in their 

 mesogloea. Their mesenterial filaments have not been repre- 

 sented, but they are still of the same nature as they were 

 higher up. The mesenteries of the fourth grade (4, 4', 4", and 

 4'") have lost all trace of their mesenterial filaments, and have 

 become very narrow. 



Figure 5 is from a region about 1.5 mm. below the preceding 

 figure. The mesenteries of the fourth grade have now dis- 

 appeared, being represented, like the ventral directives, only by 

 slight projections of the mesogloea. The mesenteries of the 

 first three grades still persist ; all are gonophoric, but all have 

 lost their mesenterial filaments. 



Still further down, in a section taken about r cm. lower, the 

 mesenteries of the third grade (3 and 3') would have dis- 



