30 G. HERBERT FOWLER. 



platte rait der Innen-platte (Theca) der vorhin beschriebenen Korallen 

 wird aus der Struktur derselben als irrig erkannt." 



The implied argument may thus be expressed in the syllogism : — 



1. The skeleton of Flabellum grows in thickness from without 

 inwards. 



2. An epitheca grows in thickness from without inwards. 



3. Therefore the skeleton of Flabellum is an epitheca — an example 

 of what is characterised by logicians as the fallacy of the undistributed 

 middle term (" Medium non Distributum "). 



Dr. von Koch is no doubt correct in asserting that the calyx of 

 Flabellum is laid down from without inwards ; but till clearer 

 evidence be adduced to the contrary, it is far simpler to regard it as 

 a theca entirely homologous with the theca of typical Madreporaria 

 (or at least with a part thereof), than to conceive that the epitheca, 

 which Ave know elsewhere only as an inconstant and inconsiderable 

 structure, should have replaced the solid theca, merely to achieve the 

 same physiological end. 



Nor is there anything in the structure of the corallum really 

 inconsistent with the idea that it is a theca. The embryonic 

 Flabellum patagonicura attaches itself to an Arenaceous Foraminifer, 

 or some similar body (vide Moseley, "Eep. Chall. Zool.," ii., Madrep., 

 pi. xv., figs. 1, 2) ; but the adult is entirely free, and therefore 

 more or less at the mercy of natural accidents such as currents. 

 Correspondingly with this condition, but unlike that of the attached 

 forms (Lophohelia, Caryophyllia, &c.) it develops no " Rand-platte," 

 (vide p. 23), but the polyp can be wholly retracted within the calyx 

 (cf. (2) Fig. 2). The absence of the " Eand-platte " implies almost 

 necessarily the absence of extracalicular calycoblasts ; the calyx must 

 therefore be deposited by those internal to the corallum. As a 

 consequence of these facts, the calyx of Flabellum, if it be not an 

 epitheca, would be homologous with that part of the theca of Lopho- 

 helia, &c, which lies internal to the dark line of growth mentioned 

 above (p. 22) ; and a comparison of Fig. 16 with Figs. 4, 5, will show 

 that there is no discordance between the two structures. 



In both forms, as is generally the case, the regions due to separate 

 centres of coral secretion are bounded by sutures ; and of these 

 regions those marked T. (theca), and S. (septal), in all three figures 

 certainly appear to be respectively homologous. Even the way in 



