THE ANATOMY OF THE MADREPORARIA. 15 



1. He states that the dark line of growth, visible in trans- 

 verse sections of the calyx, which indicates the earliest formed 

 part of the coral at that level, is in Flabellum placed peri- 

 pherally (fig. 16), and consequently that the skeleton is laid 

 down from without inwards. 



2. Elsewhere in the same paper he infers, from his researches 

 on the development of Astroides calycularis (8) that the 

 epitheca of all corals, originally deposited outside the lateral 

 body wall of the embryo, also increases in thickness on the 

 inner side only. 



3. Finally, we find that " diese Koralle bildet einen ganz 

 eigenen Typus, wegen des ganzlichen Fehlens der Innen-platte. 

 Die Aussen-platte 1 ist gut entwickelt . . . Die Homologisirung 

 der Aussen-platte mit der Innen-platte (Theca) der vorhiu 

 beschriebenen Korallen wird aus der Struktur derselben als 

 irrig erkannt." 



The implied argument may thus be 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 we know elsewhere only as an incon- 

 stant 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 patagonicum attaches itself to an Arenaceous 



1 I. e, Epitheca. 



