36 EOCENE AND LOWER OLIGOOENE CORAL FAUNAS. 



Miss Ogihne has presented no evidence that these calcareous pi'oducts 

 of the coral animal contain organic cell material, or that, there is " a car- 

 bonized residue " in the skeleton. Our knowledge of the origin of the 

 skeletal matter has not, therefore, been advanced by Miss Ogilvie's research. 



In working over my own thin sections, I have seen practically all the 

 phenomena desciibed by Miss Ogilvie, but as yet I have been unaljle to 

 institute a seiies of rigid tests to determine their meaning. 



After this paper had gone to press, Mr. Gilbert C-. Bourne's Studies on 

 the Stiiicture and Formation of the Calcareous Skeleton of the Anthozoa^ 

 came to my notice. A resiun^ of Mr. Bourne's paper can not now be 

 given here. He proves effectively that the skeleton of the Madreporaria is 

 not originated hy the calcification of ectoderaial cells, but that it is secreted Ini 

 the calicoblasts. 



THE BASAL PLATE. 



In those corals that are originally attached to some basal object of 

 support, the first-formed skeletal part is the basal plate. This was first 

 discovered and described by von Koch in his study of the development of 

 Asteroidea cahjcularis.' He secured young larvae on bits of cork, and 

 observed that the building of the skeleton is begun by the larva forming 

 " a thin circular plate, composed of round or elliptical crystal elements 

 (Krystaldrilsen), which originally have openings between them, biit these 

 soon become filled out through a further secreti( m of lime bv the ectoderm."^ 

 Von Koch states that "this first thin little plate is later more and more 

 thickened through a more or less clearly laminated deposit of new substance 

 by the ectoderm, and not seldom, even in old grown skeletons, it can still 

 be clearly shown in sections through the principal axis of the polyp." ■* In 

 examining young attached sjiecimens of corals, evgn fossil, the basal plate 

 can sometimes be clearly distinguished. PI. XXI, fig-. 12, shows a very 

 young stage of Bliectojjsamniia claibornensis, in which only the basal ])late 

 and a few septa have been developed. Quite frequently, by Ijreakiug a 

 young attached coral from its object of support, the basal })late may be 

 seen on the originally attached end of the coral. Theoretically it can not 



■ Quart. Jour. Microsc. Sci. (N. S.), Vol. XLI, Pt. IV, No. 1G4, Jan., 1S99, pp. 499-547, pis. sl-xliii. 

 - Uelier ilio Kutwickelung- des Kalkskeletcs von Asteroides calycularis uud dessen morpbologi- 

 sclier Bedeutuiig: Mittli. Zoolog. Statiou zii Neajitd, 18S2, I'l. Ill, pp. 284 to 292, pis. xx, xxi. 

 '•' Das Skelett der Steiukoralleu. Gegenbaur Kestschiil't, p. 253. 

 * Op. ot loc. 8up. cit. 



