SOLITARY CORALS. 205 



development of Balanophijllia Jloridana which, if it had received the attention it 

 deserved, would have given a full explanation of the peculiarities of the septal 

 arrangement in this genus. Pourtales' description is as follows : " The youngest 

 individuals observed have the shape of a truncated cone attached by the base. The 

 wall is (piite smooth, imperforate, and the septa, twelve in number, equal and not 

 quite extending to the centre, where the rudiments of the columella are already 



visible The next step is the formation of costee on the upward prolongation of 



the wall. They first appear in the shape of sharp points grouped about the origin of 

 the septa. At the same time an opening appeal's on the border and rather outside of 

 the calicle, opposite each of the secondary septa, which gradually widens inwards, 

 apparently dividing the septum in two. The two borders of that opening become the 

 tertiary septa ; the secondary septum is gradually pushed inwards and is replaced by 

 a new one growing out on the same radius from the wall, and but loosely connected 



with the jointed tertiaries and original secondary The interior part of the 



tertiary septum is now to all intents and purposes a palus As the growth 



proceeds the point of junction of the tertiaries and secondaries moves further into the 

 calicle until it reaches the columella. At this period the older or internal part of the 

 secondary septum has nearly entirely disappeared and the same process of growth goes 

 on with the septa of the fourth cycle which become joined to those of the third." In 

 these few sentences Pourtales anticipates the discoveries of several recent authors. 

 The imperforate wall is clearly the hasal plate of von Koch (= prototheca, Bernard). 

 The description of the formation of costre on the upward prolongation of the proto- 

 theca agrees exactly with de Lacaze Duthier's description and figures of the 

 development of these structures in Balanophijllia regia (33, plate x., tigs. 20 

 and 21). The description of the bifurcation of the peripheral ends of each secondary 

 septum, and the formation of a new secondary septum on the same radius, is in 

 exact agreement with Duerden's (9 and 10) account of the septal sequence in 

 Siderastrcea radians. But, although the credit of priority must rest with Pour- 

 tales, it is the last-named author who has given a full and perfectly intelligible 

 account of this mode of septal sequence, and has shown in detail the relation hetweeu 

 the order of appearance of the septa and that of the mesenteries. In his valuable 

 and beautifully illustrated memoir, Duerden has shown that in Siderastrcea radians 

 the six septa comprised in the first cycle appear simultaneously, and are situated 

 within the entocceles of the six primary pahs of mesenteries. The six septa of the 

 second cycle make their appearance later and occupy the six exoccelic chambers, thus 

 alternating with the six primaries. As growth proceeds the peripheral ends of all 

 the septa become bifurcated, as a consequence of the continuous addition of skeletal 

 nodules to their outer ends, but the angle formed by the bifurcating limbs is much 

 larger in the secondary (exoccelic) than in the primary (entoccelic) septa. The bifur- 

 cations become filled up and disappear in the primary septa, but in the secondaries 

 they continue to extend, and presently a second mesenterial cycle is developed, each 



