160 PROP. p. M. DUNCAN ON THE 



smaller septa, on either side of the larger, unite into one within 

 and without it, that is to say axially and circumferentially. The 

 union is by a V-shaped mass, more or less dense or merely linear, 

 of delicate reticulate tissue, the transverse parts resembling 

 delicate cross bars. The increase in numbers of septa occurs during 

 the growth of the corallum, which takes place exogenously and at 

 the circumference. As this enlarges, the septa which are radial 

 have increasing breadths between them at the edge of the coral ; 

 and in the spaces thus formed septa arise from between septa at 

 the base, and grow upwards, joining the nearest as a rule. 



In Halomitra the junction of septa is restricted to certain parts 

 of a calicular system; and the third septum of a system is the 

 aggregate of several sets of smaller septa. 



Next in importance to the septa are the structures which, 

 besides forming a large part of the base, unite the septa at their 

 sides, and in some instances the costse also. These are the synap- 

 ticula. Ovidng to the introductory statement regarding synapticula 

 by their discoverers, MM. Milne-Edwards and Jules Haime, 

 these structures are treated of by every subsequent author as 

 ornamental graniiles, wart-shaped projections, and tubercles which 

 stretch across the interseptal spaces, and unite with corresponding 

 structures on the opposite septa, and also as the hypertrophy 

 of the ordinary ornamental granulation of the sides of the septa, 

 fusion taking place at junction. 



In the FungincB these structures are only of secondary import- 

 ance to the septa ; and indeed they are more solid and stronger 

 than the higher orders of them. Moreover they modify the con- 

 dition of the lower parts of each interseptal loculus. 



Seen from above, the synapticula are in series in each inter- 

 septal loculus, and look like cross bars. Seen from the side, 

 after fracturing a coral across, the synapticula are stout, nearly 

 vertical or curved continuous ridges with a considerable vertical 

 development. Each ridge is of course a fractured synaptieulum, 

 and is followed by a corresponding groove, one side of which is 

 the septum bearing the synaptieulum, and the base of which may 

 be closed below, or it may open outwards by the perforations at 

 the base. As there is a series of the synapticula in each inter- 

 septal loculus, there is a row of these ridges extending more or 

 less from the axial space to the circumference along the septum or 

 septa (PL V. fig. 1), and each ridge is separated from its neighbours 

 by a groove. In the normal condition of the parts, each inter- 



