388 Dr. J. K. Ducvclon 071 the UAatloushipn 



tlie relationship of llie so])ta to tlie mesenteries in modern 

 corals, the larger septal series evidently appeared within the 

 entocoelic chambers of the polyps, while the smaller septa are 

 exosepta. In the early staores of recent corals it is not 

 unusual for the entosepta to appear in advance of the exo- 

 septa ; but the interval would appear to have been enormously 

 exaggerated in the present form, until, in fact, the full com- 

 plement of entosepta had appeared. 



Not only are the serial transverse sections of L. proh'ferum 

 favourable for the establishment of the primary condition of 

 the septa, as well as the sequence of the later members, but 

 the results can be confirmed in a most definite manner from 

 the well-defined ridges and grooves occurring on the outer 

 surface of the corallum. Sections through the lower part 

 of the coral demonstrate that two external ridges corre- 

 spond with each internal interseptal space, and each alter- 

 nate groove corresponds with a septum ; in the upper part 

 of the calice, where the cycle of small septa has appeared, 

 each ridge then corresponds with a single interseptal space, 

 and each groove with a septum (cp. figs 6 & 8). On 

 Sjiecimens of which the tip and the external surface of the 

 coral are well preserved twelve grooves and ridges, repre- 

 senting the six primary septa and interseptal spaces, occur 

 practically as far as the apex, and can be followed all the way 

 upwards, and the successive intercalation of the later septa at 

 four regions can also be observed (figs. 9, 10). 



All the more recent studies on the Anthozoa indicate that 

 the order of appearance and adult arrangement of the mesen- 

 teries are the surest guide to a phylogenetic or natural classi- 

 fication. In the divisions Actiniaria and Madreporaria, 

 including the sea-anemones and corals, two sharply distin- 

 guished stages in the appearance of the mesenteries are to be 

 recognized, the one embracing the development of the six 

 primary jiairs of mesenteries ( protocnemes) and the other the 

 development of all the later mesenteries {metacnemes). With 

 a i^w exceptions the order of establishment of the six pairs 

 of protocnemes is the same throughout the Actiniaria and 

 Madreporaria, denoting these two to be a well-defined, primi- 

 tively hexamerous group. With the appearance of the later 

 mesenteries, however, divergences are introduced which are 

 to be regarded as of the most fundamental importance in 

 actinian and coral morphology. 



Three distinct types of mefacnemic succession are recog- 

 nizable. In by far the majority of recent corals and anemones 

 the new mesentt-ries arise successively as unilateral pairs 

 within each of the six primary exoccelic chambers, and in the 



