48 J. E. DUERDEN. 



I refer to them here, although not directly bearing upon the fos- 

 sula. He makes the supposition (p. 1 1) that "The falling over 

 of the prototheca will explain the departure from a strictly radial 

 symmetry of the septa seen in these curved Palaeozoic corals." 

 He also remarks : " Further, it has long been known that, as 

 such corals gradually reacquire a vertical position, the septal 

 arrangement slowly gives up the bilateral and returns to the 

 radial symmetry. Thus the character on which it was proposed 

 to found a great division of the stony corals was nothing but a 

 slight mechanical adaptation to a passing phase in the life of each 

 individual coral. But it is only fair to say that the whole tend- 

 ency of recent works on corals has been to discover the invalidity 

 of the supposed division Tetracorallia." 



In a previous section (p. 42) I have dwelt upon the significance 

 of bilateral and radial symmetry in corals, and have shown that 

 in both modern and fossil corals the developmental stages 

 throughout are bilateral, and that it is only towards maturity that 

 the most nearly perfect radiality is assumed. It is the order in 

 which the mesenteries and septa appear in corals which gives 

 their distinctive significance to modern and extinct forms, not 

 their bilateral or radial symmetry. Even the first six pairs of 

 mesenteries which arise before any skeleton appears are arranged 

 in a strictly bilateral manner in modern corals, and the subse- 

 quent mesenteries and septa also follow the bilateral plan. When 

 fully developed the majority of rugose corals are as perfectly 

 radial as are modern corals. The statement "that the whole 

 tendency of recent work on corals has been to discover the in- 

 validity of the supposed division Tetracorallia" is made on only 

 a partial view of the case. The only recent discovery of any 

 importance in support of Bernard's position is the demonstration, 

 mainly by Miss Ogilvie, of the unity of microscopic structure of 

 the skeleton of rugose and modern corals, a discovery which was 

 to be expected considering that the polyps forming the two groups 

 of skeletons belong to one group, the Zoantharia. Even the dis- 

 covery by the " Challenger" of the coral Moscleya, which, from 

 Quelch's account, was hailed as a living representative of the Tet- 

 racoralla, and as breaking down their distinction from living 

 corals, is shown in Bernard's present paper (p. 24) to be alto- 



