THE STEUCTUEE OF POEITES. 495 



to the finer texture of the walls which are built out of these 

 septa, with their synapticular junctions. 



It is quite correct to say otPorites that the stiff radial and 

 concentric symmetry of septa and synapticulse which characterizes 

 the typical Madrepore is here melted down into a reticulum ; 

 a reticulum more loose because of the perforate and incomplete 

 character of the septa. 



We find, however, interesting variations in this respect. Not 

 a few Porites still show traces of the stiff radial septa radiating 

 outwards on the top of the walls as so many short ridges, e. g., 

 slightly seen in fig. 4, PI. 35. These sometimes run from calicle 

 to calicle, but are always slight and never approach the fine 

 systems of parallel strige which are so well developed over the 

 whole coenenchyma in Madrepora and Turhinaria, as unmistakable 

 evidence of the part which the laminate septa (or costae) play in 

 the construction of the walls. 



The first stage of dissolution is probably that in which the 

 vertical elements persist as trabeculge or upright threads which 

 end above the surface as granules. This is the most common 

 condition of the surface of Porites. The connection between the 

 walls can then be seen from the fact tliat the wall granules are 

 only a repetition of those seen within the calicle — septal granules 

 and pali. 



Not infrequently the horizontal elements become flattened 

 flakes, so that the vertical section shows tiers of floors supported 

 by short pillars. 



The last stage is that in which both vertical and horizontal 

 elements melt down entirely into either a sponge-work, or into a 

 system of flakes mostly lying horizontally. In these cases we 

 do not usually find the surface covered with granules, they 

 are present only so far as the vertical elements, the tips of 

 which constitute these surface -granules, continue to be developed 

 as pillars. 



The ColumeUar Tangle and Tubercle. — The base of the calicle in 

 Porites always fills up sooner or later with a mass of reticular 

 tissue, as emphasized by Dana*. This tissue may be conveniently 

 called the ColumeUar Tangle. The most symmetrical manner in 

 which this can develop is as a regular ring joining the septa and 

 pali. It rises to various heights. It may be very simple and 



* Zoophytes, 1848, p. 117. 



