OLA881 ANTHOZOA 



l>;iii- of mesenteries, the infold. -.1 ectoderm secrete* siu;ill, round, oval, or irregular 

 calcareous bodies (ackrtfea); these arejojjjysed against one another in radial 

 direction-, and as oth. cessTvely hid down on the top of them, upright 



partitions in- sep^d^Sternleisten, downs) are built up! Gradually, also, as the 

 p..lvp approaches maturity, the ba-al plate becomes ral-ilied. owing to the 

 georetion l.y the outer surface of the ectoderm of numerous minute, cWly 

 crowded, calcareous bodies. The septa, however, grow considerably above the 

 Itase. and become lodged in the vertical interspaces between the mesenteries. 

 In the same manner, within the soft body- wall, a calcareous secretion may 

 take place, bind in- the outer edges of the septa together, and known as the 

 n',ill or tli.rn (M'U/n; H'miil. ntiiniillr). Both septa and theca are composed of 

 minute, denselv crowded calcareous bodies, in which delicate calcareous fibres 

 may be seen radiating in all directions from a central dark space. And since 



- - 



i:i,r<iir,mn ruiirmn, j^uin. (after Lacaze-Dnthiere). 



Mrancli of red coral of roimm'rrc laid K\-U alon^ 

 1 IP- axis, and showing tlifi'i' jtulyjis in sci-tion IMII- 

 lit-ddi'd in rtt-shy cijfiiosark. 



FIG. 101. 



Astroiil' 1 * I'liii/ciiinri*. l.amx. sp. Mediterranean 

 (after Lacaze - Duthiers). Enlar-fd longitudinal 

 section of polyp with calcareous skrMon. te, T'-i;- 

 tacles ; oe, Oesophagus ; i>, Mesentery ; loc, M> 

 tt-rial pouches ; coe, Coenosark ; .^>t, s.-ptum : 

 col, Cohuiiella. 



all the calcareous bodies forming the septa have a radial disposition, the 

 calcification-centres as seen in transverse sections form a dark, mostly inter- 

 rupted, and occasionally jagged median line, from which bundles of minute 

 fibres radiate outward in all directions. Similar calcification-centres are found 

 also in the theca. Sometimes the median dark line is uninterrupted and 

 di\ ides the septum into two separate lamellae. 



The interstices between the sclerites forming the septa are either completely 

 filled with carbonate of lime (Aporosa), or there remain larger or smaller porous 

 -paces (J'l'i-furnta); in many cases, in fact, the septa are represented by a loose 

 network of sclerites piled up vertically, or merely by vertically directed spine-. 



The number of mesenteries and septa within the visceral chamber is equal 

 to that of the tentacles, and is somewhat uniform throughout the different 

 sub-classes, orders, genera, and species. Increase takes place, as a rule, in such 

 a manner that whenever, as the polyp grows, a new visceral chamber is formed. 



