Vol. 69.] THE GENUS AULOPHYLLUM. 75 



The minor constrictions of the corallum, shown in text-fig. 1 

 (p. 58), which are so marked a feature in most Rugose corals, are 

 very similar to those resulting from rejuvenescence ; but they are 

 much less pronounced. They do not appear, however, to be 

 accompanied by any changes in the internal structure of the coral, 

 except in the width of the dissepimental zone : unless the irregu- 

 larities observed (p. 59) in the width of the central column bear 

 some relationship to them, but this connexion is not at all obvious. 

 Nevertheless, the contractions of the dissepimental zone probably 

 originated from the . same zone as rejuvenescence — possibly con- 

 traction on the part of the polyp itself. It may be suggested that, 

 if the contraction of the polyp was carried beyond a certain point, 

 it resulted in the structural changes in the corallum just described. 

 Such extreme cases, it would seem, are comparatively rare. This 

 suggestion is not necessarily antagonistic to Bernard's theory. 



The reduction in the width of the corallum, the central column, 

 and the dissepimental zones, and in the number of the septal 

 lamellae, also the straightening-out of the pericentral vesicles, 

 recapitulate the characters of the younger stages of growth. 



EXPLANATION OF PLATES V-IX. 



[The sections are now preserved in the British Museum (Natural History), 

 South Kensington.] 



Plate V. 



Aulophyllum fungites (Flem.). Sections illustrating ontogenesis 

 and phylogenesis. All from Peterhill Quarry, Bathgate. 



Fig. 1. Transverse section at the conclusion of Stage A. The six primary 

 septa have been inserted ; and the first two of the secondary septa 

 are appearing at the alar fossula3 A and A', and marking the 

 commencement of the Zaphrentoid Stage. (C = cardinal septum; 

 A and A' = alar fossula? ; K. = counter-septum.) X 4. 



2. Transverse section at the conclusion of Stage B. The separation of 



the septa at the centre and the presence of a rudimentary central 

 column indicate the passage into Stage C. X 4. 



3. Transverse section, Stage C, early phase. Septa penetrating the 



central column. Large cardinal fossula, X 4. 



4. Transverse section, Stage 0, later phase. Most of the septa are 



free from the central column, and the cardinal fossula is not so 

 prominent as in fig. o. X 4. 



5 a . Transverse section, Stage D. The central column has the character of 

 mut. redesdcdense. x 1"5. 



5 b. Transverse section, Stage E. X 1*5. 



5 c. Transverse section, Stage F, showing the characters of mut. pachy- 

 enclothecum. X 1'5. 



6. Transverse section, mut. redesdcdense. Fourlaws Limestone, Water- 

 falls Quarry, near Redesdale (Northumberland). X 1'5. 



7 b. Transverse section, ' tortuous ; type. Mut. paehyeiidotheeum. 



7 a. Earlier transverse section of the same individual at Stage E, showing 

 the subquadrate aspect of the central column. 

 Figs. 8 & 9. Transverse sections, mut. pachyendotheeum, showing different rates 

 of growth. Fig. 8 is cut at 5 cms. and Fig. 9 at 8 cms. from the 

 proximal end of the coral. Both figures are of the natural size. 



