THE ANTHOZOA 63 



the bottom of the calycle and project between the inner edges of 

 certain septa and the columella. In addition to these parts, other 

 structures are found in the skeletons of certain corals. Dissepi- 

 ments are oblique calcareous partitions stretching from septum to 

 septum, and closing the interseptal loculi below (see Fig. XXXI. 

 2). The whole system of dissepiments in any given calyx is often 

 called endotheca. Synapticula are calcareous bars uniting adjacent 

 septa (Fig. XXXI. 3). Tabulae are stout horizontal partitions 

 traversing the whole space within the calycle. 



Though the skeleton or corallum of the Scleractiniae appears 

 to lie within the zooid, it is morphologically external to it, as is 

 best shown by its developmental history, which has been studied 

 by G. von Koch in Astroides calicularis (55) and in Caryophyllia 



Fio. XXIX. 



Radial section of the larva of Astroixies calicularis, which has fixed itself on a piece of cork. 

 ec, ectoderm ; en, endoderm ; mg, mesogloea ; mm, mesenteries ; S, septum ; B, basal plate, 

 formed of ellipsoids of carbonate of lime secreted by the basal ectoderm ; cp, epitheca. (After 

 G. von Koch.) 



cyathus (105), and by H. V. Wilson in Manicina areolata (98). 

 The larvae of Astroides are at first ciliated and free-swimming, 

 and do not acquire a corallum until they fix themselves. The 

 first trace of the corallum appears as a ring-shaped plate of cal- 

 careous tissue situated between the basal ectoderm and the surface 

 of attachment. It is composed of calcium carbonate in the form 

 of numerous spheroidal masses of concentric structure, each mass 

 built up of numerous rhombic crystals. Von Koch states definitely 

 that the calcareous nodules are formed as a secretion product of 

 the ectoderm, and he gives figures which fully bear out his assertion 

 (Fig. XXIX.) Wilson, as far as he has traced the development of 

 the corallum in Manicina, confirms von Koch's statement. Von 

 Heider, however, holds that the calcareous crystals are formed 

 within ectodermic cells, as are the spicules of Alcyonaria, but his 

 proofs are not satisfactory. 1 The further development of the 

 corallum is effected by the completion and increase in size of the 



1 Since this was written, Dr. Maria M. Ogilvie has expressed herself strongly in 

 favour of von Heider's opinion. The subject requires reinvestigation, but it must be 

 said that Ogilvie's evidence is not strong enough to overthrow the positive embryo- 

 logical observations of von Koch and H. V. Wilson. (The writer has since shown 

 that von Koch's views are correct and that no true spicules, formed within cells, 

 occur in the Scleractiniae. Quart. Jour. Micr. Sci. vol. xli.) 



