130 EXPLANATION OF PLATES. 



Plate ii. 



Fig. 66. Tran.sverse section tlirousjh a single trabeciila, penetrated by filamentous boring algaa, and 

 showing the growth lamellre and their fibrous character. 



Fig. 67. Vertical section through a part of two adjacent septa. The septa are made up of trabeculae 

 arranged in a radiating manner ; they diverge from a continuous median trabecula which represents the 

 boundary between the two adjacent calices. The different appearances presented by the various trabec- 

 ule are dependent upon the part included in the section. Where the section passes along the middle of 

 a trabecula the interrupted dark centers of calcification are seen ; elsewhere only the diverging bundles of 

 fibrocrystals appear. The growth lamellss are not shown (c/^ fig. 68). New trabeculie are intercalated 

 at intervals. The dark circular and oval patches are sections of synapticula. 



Fig. 68. Terminal portion of two trabeculae as seen in longitudinal radial section, that is, parallel to 

 the surface of the septum, more highly magnified than in the previous figure. The section passes along 

 the middle of the trabeculse so that all the dark centers of calcification are seen. In the corallite from 

 which the section was taken the growth lamelloe were very distinct, the boundary of each being indicated 

 by a dark granular deposit similar to that at the centers of calcification. The growth lamelliB are arranged 

 parallel with the toothed edge, that is, with the calicoblast layer which secretes them, while the fibro- 

 crystals making up the lamella are arranged at right angles. The figure should be compared with fig. 

 66, which shows a trabecula in transverse section. 



Fig 69. Portion of basal plate and epithecal boundary of a very early corallum. The epitheca is seen 

 in section, and the basal plate is sufficiently thin to allow of the passage of light. The basal plate is made 

 up of more or less distinct granules or scales showing a fibrous structure; the aggregation of darker 

 granules represents the first formation of a septum. 



Fig. 70. Portion of basal plate, septa, and epitheca of a somewhat older eorallum than that of fig. 69. 

 The sepia and epitheca are ground down to nearly the level of the basal plate Centers of calcification 

 are not present in the basal plate and epithec^i but are very prominent in ihe septa. 



