308 GILBERT C. BOURNE. 



lines of calcareous crystals ; these are the first rudiments of 

 the septa. At a later stage the septa form proportionally high 

 plates^ over which the ectoderm is bent in the form of a fold, 

 the septa begin to branch at their peripheral ends, and 

 eventually these branches meet and fuse with one another to 

 form the theca, which cuts the mesenteries in two portions 

 and isolates the more peripheral part of the ccelenteron from 

 the more central, the former being limited externally by the 

 soft body wall, which at first extends down to the base of the 

 theca. One might almost speak of the corallum as being 

 pushed in from below, all the three body layers being invagi- 

 nated to receive it. Eventually the ectoderm which is bent 

 over the corallum, having the sole function of secreting cal- 

 careous matter, comes to be represented by that layer of cells 

 lying between the mesoglcea and the corallum, to which von 

 Heider has given the name of calycoblasts. In old specimens 

 the external body wall becomes atrophied around the lower 

 part of the calyx, wliere it is physiologically replaced by the 

 theca, but it still holds its place as an investment of the upper 

 part of the calyx (Eandplatte of von Heider) (14). The young 

 nurse-stock of Fuugia, so long as it remains cup shaped, has 

 all the characters of a Gary ophy Ilia, and may be compared 

 strictly with the young Astroides. Stutchbury (39) says of 

 it, " So long as the young Fungia retains the form of a Caryo- 

 phyllia it is entirely enveloped by the soft parts of the animal, 

 but as the upper disc of the coral spreads out and assumes its 

 characteristic form, the pedicle is left naked and the soft parts 

 extend only to the line where the separation afterwards takes 

 place." In the '' Alert ^' specimen in the British Museum the 

 soft parts still extend to the base of the nurse-stalk, although 

 the upper disc has begun to widen out. When the young 

 Fungia separates from the nurse-stock a clean scar is left at 

 the point of detachment, through which there is for a short 

 time free communication to the interior. But the deposition 

 of calcareous matter round the central ends of the septa soon 

 blocks up this passage, and immediately afterwards the soft 

 parts covering the theca (which is now nearly confined to the 



