CORALS 



of a foot or two in diameter. The surface of the branches 

 is rough owing to the presence of a number of minute spines 

 or tubercles on the surface, and the calices are very small, 

 their appearance being represented by holes or pits usually 

 flush with the surface. There is of course some variation 

 in the size of the calices, but it may be found that in a large 

 collection of specimens the average diameter of the calices 

 at the margin is less than i mm. 



These characters can be easily determined, but there are 

 some very important ones which require careful observation 



and manipulation of the light 

 to be clearly demonstrated. 



In many dried specimens 

 there seem to be no septa at 

 all even when the calices are 

 examined with a magnifying 

 glass. This may be due either 

 to the presence of the dried 

 remains of the polyp tissues, 

 which obscures the septa, or to 

 the calyx examined being old 

 and water-worn with the septa 

 partly destroyed. To examine 

 the septa, smaller terminal 

 branches should be thoroughly 

 cleaned by boiling in 5 per 

 cent, potash for some time and 

 then dried and examined in a good light, on a black ground, 

 with a pow'erful lens or low'-power microscope. It is only by 

 such means that it can be definitely ascertained that there 

 are nearly always twelve small septa, of which six may be 

 complete and six incomplete. Moreover, of the six complete 

 septa two are larger than the others and form a pronounced 

 ridge on the floor of the cup. These two septa are the 

 directive septa and they always lie in a plain parallel with 

 the axis of the branch. 



The next two points to determine require the examina- 

 tion of a transverse section of a thick branch or the exposed 

 surface of a freshly made fracture. It may then be seen 



Fig. 34. — Seriatopora. A few 

 terminal branches of a large colony. 

 Nat. size. 



