REPORT ON THE ANTJPATHAUI A. 



37 



twelve mesenteries are present, enclosing twelve interseptal chambers of the ccelenteron. 

 In this region the mesenteries are so disposed that an interseptal chamber is situated at 

 each end of the sagittal axis of the mouth, and the middle of each wall of the mouth is 

 also bordered by an interseptal chamber. In other words, both the sagittal and median 

 transverse axes correspond with interseptal chambers instead of mesenteries. The 

 mesenteries are here all equally developed, and consist of a delicate plate of mesoglcea 

 lined on each side by entoderm. Each quadrant of the oral cone contains three mesen- 

 teries, two complete interseptal chambers, and half each of a chamber in the sagittal and 

 another in the median tranverse axis. For convenience of description, the mesenteries 

 have been numbered from 1 to 12 in fig. 16, which is diagrammatic. A few sections 

 lower down, the arrangement just described becomes changed. The mesenteries numbered 



Fig. 1. Fig. 2. Fig. 3. 



Figs. 1-3. — Horizontal sections of Leiopathes gldberrima. 



Fig. 1. — Section through the upper portion of the oral prominence, passing also through the two pairs of lateral tentacles. 

 Fig. 2. — Section near the base of the oral prominence, showing the lumen of each of the four lateral tentacles opening 



circumoral sections of the ccelenteron. 

 Fig. 3. — Section in a plane beneath the insertion of the sagittal tentacles, showing the six primary mesenteries projecting 



ccelenteron ; those in the transverse axis are most important. 



into the 

 into the 



4 and 9 in fig. 16 lose their connection with the wall of the oral cone, and become lost, 

 and those numbered 3 and 10 now become gradually more important, and change their 

 position so as to occupy the median transverse axis. This arrangement is represented 

 in fig. 2, which is taken from a horizontal section passing through the base of the lateral 

 tentacles. A little further down four other mesenteries, viz., numbers 2, 5, 8, and 11, 

 lose their connection with the outer wall, and after persisting for a short distance as 

 projections from the wall of the stomodseum, ultimately disappear. In the lower portion 

 of the stomodseum (fig. 3) only six mesenteries remain, namely, those numbered 1, 3, 6, 

 7, 10, and 12 in fig. 16. These are the mesenteries referred to as "primary." The 

 transverse primary mesenteries are most important, and bear the reproductive organs 

 as well as a well-developed convoluted mesenterial filament. The other primary 



