146 CORALS 



In many specimens, and particularly in the older parts 

 of the corallum, the pores are arranged in circles — called the 

 cyclo-systems — a single gasteropore in the centre of the 

 circle and a ring of five to seven dactylopores around it. x^t 

 the growing edges of the fronds or branches and all over the 

 surface of some specimens the pores seem to be much more 

 irregularly scattered. The arrangement of the pores in 

 cyclo-systems must not, therefore, be regarded as an in- 



FiG. 66. — Millcpora. A part of a frond of a large colony, showing the spores 

 arranged in regular cyclo-systems. Xat. size. 



variable character of the corallum of Millepora. Occasion- 

 ally there may be found in museum collections specimens 

 of the coralla of Millepora which look as if they were afflicted 

 with a disease or were otherwise abnormal (Fig. 68). They 

 exhibit all over the surface, or on some parts of it only, a 

 number of shallow, blister-like cups having a diameter about 

 twice that of the gasteropores. These cups are the Am- 

 pullae, and it is now known that they are the receptacles 

 of the medusae which bear the eggs or sperms.^ They are 



1 S. J. Hickson, Proc. Roy. Soc, vol. l.xvi., 1899. 



