72 mk. Stanley smith on [March 19 1 3, 



IX. Stereoplasmic Thickening. 



The septa and vesicles are usually stouter at one part of the 

 corallum than at another, owing to the greater development 

 of the ' stereoplasmic ' layers. At the proximal end the theca and 

 septa are as a rule extremely thick in proportion to the size of the 

 corallum. The septa which have originated at the cardinal f'ossula, 

 even at the earliest stages, are thicker than those of alar-fossula 

 growth (PI. V, figs. 3 & 4), and later this distinction becomes 

 more marked. The thickening, however, is confined to the zone of 

 tabular vesicles, and is not continued through the outer dissepi- 

 mental zone (except at the cardinal fossula). The tabular vesicles 

 of the cardinal quadrants share the thickening, although the outer 

 dissepiments are not usually affected, except the innermost cycle, 

 which is often intensified to the extent of forming a boundary- 

 wall. The microscopic structure of the thick septa does not differ 

 from that of the thinner septa. 



This greater development of stereoplasm on one side of the 

 corallum than on the other is a normal and distinctive character of 

 many Rugose genera. 



Occasionally excessive thickening of tissue affects the whole 

 coral or some particular part. The pericentral vesicles are, in some 

 individuals, fused together into a thick solid wall. In a specimen 

 from Anglesey, the tissue within the central column in the upper 

 part of the coral was affected to such a degree by the accretion of 

 stereoplasm, that its true nature was entirely masked. These 

 cases indicate an abnormal condition on the part of the coral. 



The tissue in well-preserved Rugose corals displays the same 

 fibrous structure as do recent Aporosa species — fibres radiating 

 from a medial line, but the structure has in many cases perished. 

 In the latter case the septa and vesicles appear under the microscope 

 as ill-defined lines in the matrix, and are crossed by the same 

 cracks and cleavages as it is. 



PI. IX, fig. 4 represents a magnified vertical section ( X 5) 

 showing the thickened septa of cardinal-fossula origin and the 

 unaffected alar septa in juxtaposition. 



X. Rejuvenescence. 



Mr. W. D. Lang, 1 in a recent paper, summarizes much that has 

 been written on the subject of rejuvenescence, and gives a useful 

 list of references to the observations and conclusions of previous 

 authors. Hence only a few remarks are needed to preface this 

 short account of the phenomenon as exhibited in a number of 

 Aulophylla that I have examined. 



The term was introduced by R. P. Tomes, 2 who translated 



1 ' Growth-stages in the British Species of the Coral Genus Parasmilia ' 

 Proc. Zool. Soc. 1909, p. 285. 



2 ' On the Madreporaria of the Inferior Oolite of the Neighbourhood of 

 Cheltenham & Gloucester ' Q. J. G. S. vol. xxxviii (1882) p. 409. 



