•46 



The general structure of the polyp may be best seen by 

 reference to Figs. III. and IV. The corallite has 1 2 septa 

 fusing by trabeculae in the axial fossa, the septa of cycles I. 

 and II., alternating with the 12 septa of cycle III., which are 

 ■extremely small, only just having made their appearance. 

 The stage then is about that shown in fig. 14. The mesen- 

 teries number 24, 6 pairs of larger situated on either side of 

 the primary septa and 6 pairs of smaller against the 

 secondary septa. The filaments of the former mesenteries 

 form great bunches of coiled loops, but of the latter are very 

 slightly developed (Fig. IV.) In one or two of the exocoeles 

 traces of the tertiary mesenteries are found in prolongations 

 of the stru :tureless lamella, which have as yet no trace of 

 filaments. 



All the mesenteries are attached above to the body wall, 

 which forms a rim around the mouth of the corallite of about 

 one-fifth its breadth. The mesenteries hang from this, their 

 free edges being continuous with its edge (Fig. IV.), but their 

 filaments do not appear until some little distance below the 

 same. On the larger mesenteries the muscular filaments 

 have developed in the typical manner, most originating near 

 the edge of the body-wall ; on the smaller mesenteries they 

 are as yet scarcely noticeable. There is no trace of any 

 tentacles in any area of the body-wall, having neuiatocysts or 

 vtherzvise, nor of any stoinodoeimi. 



Fig. IV. Diagrammatical longitudinal section through, the attached post- 

 larval stage of F. ruhrum described in the text. The left side represents one of the 

 mesenteries hounding a primary septum, and on the right side mesenteries bound- 

 ing secondary and tert'ary septa are shown. 



A. — D. sections shown in Fig. III. 



e. IV. External body- wall. m. /. Mesenterial filaments. Wi, w), and ?;^3. 

 Mesenteries bounding septal cycles I., II. and III. Si, S^ and So.. Septa of cycles 

 I., II. and III., represented by incomplete lines. T. Trabeculae from the septal 

 es. E. Epitheoa. P. Basal plate. 



