bo 
Wo) 
i) 
MR. W. D. LANG ON GROWTH-STAGES [ Mar. 2, 
V. REJUVENESCENCE AND TABULA- FORMATION. 
Bernard *, who put forward this explanation of Rejuvenescence, 
goes further and suggests that tabula-formation has a similar 
origin. This is in direct contradiction to the generally accepted 
idea that tabula-formation is only a more complete form of dis- 
sepiment-formation ; that whereas the latter only expresses a 
frequent and partial recession of the soft parts from the lower 
portion of the skeleton as the coral grew upwards, so tabulee 
express a periodic upward retreat of the soft parts as a whole. 
This may well be the origin of tabule (dissepimental tabula) in post- 
Rugose Madreporaria, the apparent tabule of which in many cases 
seem to be modified dissepiments and often are seen to accompany 
the reduction of septa. This is so in a series of Bathonian species 
placed in various genera, but all allied to Cyathophora and Crypto- 
cenia, of which a series is exhibited in the British Museum. 
These show the tendency to lose their septa and convert the 
interseptal dissepiments into tabule. Intermediate forms occur 
between Cyathophora prattt Kdwards & Haime, with well developed 
septa and few large dissepiments which tend to correspond with 
similar ones on the other side of the corallite, and Astrea bowrgets 
Defrance, in which the septa are only ridges and there are clearly 
marked tabule. Holocystis elegans (Fitton), from the Lower 
Greensand, has tabule and reduced septa, and the same is true of 
the Paleozoic Tabulate corals. That tabula-formation of this 
origin may have followed and replaced their formation from a 
transverse fission 1s possible; but the two methods are essentially 
distinct and mutually exclusive. The recapitulation of earher 
stages might be used asa test to determine which cause is operative 
in any case, for there is no reason to suppose that it would occur 
merely on the upward movement of the coral in its skeleton; while 
it has been shown to occur as an accompaniment of rejuvenescence. 
VI. AstoGENy AND Hisronysis. 
Before leaving the subject of rejuvenescence connected with 
fission in a horizontal plane, it is interesting to note that Bernard 
claims a similar behaviour in the coral colony to that m the indi- 
vidual. Colonies of corallites, he says (that is, whole corolla), 
undergo rejuvenescence, forming the well-known masses of coral 
in cake-shaped pieces piled one on the other (metamerically seg- 
mented, Bernard suggests), or else branched in regular order of 
repetition. And he mentions an observation by Duerden { of a 
living form which suggested that at the periods of rejuvenescence 
a general histolysis took place in the coral mass, representing col- 
lectively the fission of each individual. Again, the Polyzoa afford 
* H. M. Bernard, 1906, Joc. cit. p. 23. 
+ H. M. Bernard, 1906, British Museum Catalogue of Madreporarian Corals, 
vol. vi. top of p. 24. 
~ Duerden, 1904, “The Coral Siderastrea,’ Washington, Carnegie Institution 
( tide Bernard). 
