FAMILIES AND GENERA OE THE MADREPOEARIA. 



201 



to each system, and in all 24. These, added to the previously existii^g 24, 

 make 48 as the number of the entire four cycles of septa. 



The fifth cycle has its septa in the intervals between the already existing 

 septa, and when it is complete the number of all the septa in Ihe corallite 

 is 96. The sixth cycle, if complete, gives 192 septa. 



The septa which arise simultaneously, in the different systems, are of the 

 same order. There is not much occasion for this term until the fourth cycle 

 of septa is considered. The septa often do not all arise spontaneously, and 

 then the fourth and fifth orders become of importance. 



There is some discrepancy of opinion regarding the exactitude of the 

 statements of Milne-Edwards and Jules Haime, but this succession is in 

 the main true, and especially in calices which are symmetrical and circular 

 in outline. Ellipticity of outline appears to interfere with the normal 

 increase of the septa, .or abnormality det^elops the ellipticity. 



In some genera the six systems do not occur, and the septa may be in 

 3, 4, 5, 6, 7, 8, 10 systems. In each of these systems, however, there may 

 be a normal succession of septa. Occasionally septa abort ; and, on the 

 other hand, one or more may be unusually large. 

 Pali. Pali or paluli are laminae or plate-like growths which extend upwards 

 from the bottom of the corallite to the ealice, where they usually project 

 between the inner edge of certain septa and the columella or the axial space. 

 They are placed before certain cycles or orders of septa only. There mjiy 

 be one or two sets or crowns or even more of them, as they are placed 

 before (or between the centre of the corallite and the septal end) several 

 cycles of septa. They differ in structure from the septa. 



Columella. A structure which fills the axis of the corallite more or less. It 

 may be solid, and may arise from the base of the corallite within, and 

 reach up to the calice and end in a knob or point. It is then essential 

 and styliform. 



It may arise from the base, and be formed of ribbon-shaped lamin£e more 

 or less intertwisted, and reaching up to the bottom of the calice. Such a 

 one is essential and trabeculate. 



It may be made up of trabecule springing from the base and ending 

 upwards with a spongy or papillary top. It is then essential, spongy, or 

 papillary. Sometimes the columella arises from the junction in the middle 

 line of processes or trabecul£e from the ends of the septa. It is then not 

 essential, hut parietal. This form may be very slight or rudimentary. 



The essential columella may sometimes be a long solid lamella, and then 

 the columella is said to be lamellar. 



It may happen that there is no columella, and then the central axis i** 

 vacant. 



Calicular axial fossa may be wide or narrow, circular or elongate. Caliculnr 

 fossa is the depth of the whole calice. 



CostcB. Projections upon the corallite or colonial wall or plateau-base with 

 intercostal depressions or spaces. Usually the costie correspond with the 

 septa; but sometimes they relate to the interseptal space or differ in 

 number. The costae may be directly continuous with the septa at the calicular 



LINN. JOURN. — ZOOLOGY, TOL. XYIII. 14 



