DEVELOPMENT OF AGAKICIA. 



507 



living polyp showing the positions of the mouth and mesenteries. 

 When the polyp was killed and the soft parts macerated it was found 

 that this drawing could be fitted with certainty over a drawing of 

 the skeleton (Fig. 5), owing to the exact correspondence between the 

 periphery of the basal plate and the outline of the soft parts of the 

 polyp. The drawings show that the primary entosepta lie between 

 the primary mesenteries and, when compared with the photograph 

 (Plate 5, top figure), that the thickenings of the basal plate re- 

 ferred to above coincide exactly with the areas enclosed in the primary 

 entocoels. 



It will be noticed in both photograph and drawing that the primary 



Figure 5. Agaricia fragilis. Outline drawing of a young polyp, showing 

 the six pairs of primary mesenteries and the opening of the mouth, superposed 

 on a drawing of the skeleton of the same polyp (septa in solid black) made 

 separately after the polyp had died and disintegrated, vi, m, median septa, 

 I, l, lateral septa. 



septa show bilateral symmetry in their arrangement and form. Un- 

 fortunately it was not possible in the living polyp to distinguish a 

 dorsal from a ventral side. That the axis of this symmetry is, how- 

 ever, dorso-ventral is shown by the oral aperture, which has its long 

 axis in this direction. The axis of symmetry is occupied by two en- 

 tosepta, which will be called median (Fig. 5, m) ; the upper (in the 

 figure) lateral septa (/) make equal angles with the median plane. 

 This is also true of the lower lateral septa, but the angle which the 

 latter make is less than that made by the upper septa. All four of 

 these septa are concave toward the upper side of the figure. 



