(Plate 10), or where considerable outgrowth takes 

 place it may eventually become convoluted as in the 

 brain-corals (Plate 14). 



In most corals, as the individual polyp continues to 

 grow, its cup becomes longer and more tubular. At 

 the same time the polyp branches to form daughter 

 polyps and the original cup now becomes two. As the 

 process continues the older part of the tube is cut off 

 by transverse partitions and a chambered mass of lime- 

 stone rock is developed (Figure 11). When the polyps 

 are only loosely connected a branched structure results 

 (Plates 22, 41). 



In other cases the polyps may remain close together 

 and the cups become united into a compact mass. (Fig- 

 ures 11, 12 and Plate 25) Sometimes the coral mass 

 itself is branched, with small cups projecting over the 

 entire surface as they bud off from the main polyp 

 (Plate 2) . 



Thus, in various ways, the small anemone-like polyp 

 eventually forms large masses of rock of considerable 

 weight, with the overall production running into bil- 

 lions of tons each year. The stony rocks developed by 

 the polyps vary greatly in appearance from small, deli- 

 cate cups to treelike branching colonies or enormous 

 boulders. 



In addition to the folds of skin which form the septa 

 or radial plates, the coral polyp possesses another type 

 of internal fold. The second t3^pe, known as a mesen- 

 tery, is an infolding of the inner lining only. For the 

 sake of simplicity they have been omitted from the 

 previous diagrams. 



During the breeding season the eggs and spermatozoa 

 begin to develop in the swollen edges of the mesentery. 



45 



