174 ON THE POSTEMBRYONIC DEVELOPMENT OF CYCLOSERIS. 



themselves fused to the secondaries. A few synapticula — formed apparently by the fusion 

 of spines on the sides of the septa — are found close to the axial fossa, which begins 

 to attain its adult appearance, closed in below by a spongy, trabecular columella with 

 small, blunt, papilliform projections. 



Another anthocyathus (Fig. 23), about 13 mm. across the calice, on an anthocaulus 

 with three rings, attached to the same dead Cycloseris as the first three instars, shows 

 the still further horizontal growth. Four cycles of septa are complete and the fifth 

 nearly so ; all are slightly exsert. 



The theca is imperforate in all the specimens; it is formed in the same way 

 as in Fnngia by the fusion of the swollen-out .sides of the septa. Fresh centres of 

 calcification appear to be intercalated as the circumference of the calice becomes 

 greater and the distance between the septal ends is increased ; these give rise to 

 the fresh cycles of septa. Some of the septa in the last instar are over 1 mm. 

 exsert while in the adult none project for more than 3 mm. beyond the theca. 

 The synapticula vary extremely, but in no specimens extend within 2 mm. of the 

 edge of the theca. 



The remaining fixed specimens are (i) an anthoblast (or trophozooid), 13 mm. in 

 diameter, but very irregular, with 4 complete cycles of septa and the fifth cycle nearly 

 complete (Fig. 24) ; (ii) an anthocyathus on an anthocaulus, attached to a bud from a 

 dead free form, 17 mm. in diameter, with 5 cycles and a few septa of the sixth (Fig. 22); 

 (iii) an anthocyathus on an anthocaulus with two rings, 26 mm. in diameter, with 

 6 cycles ; (iv) an anthocyathus on a trophozooid, 31 mm. in diameter, with 6 cycles and 

 a few septa of the seventh (Fig. 21); (v) a very irregular anthocyathus on an antho- 

 caulus, 37 mm. in greatest diameter, with 6 cycles and in places the seventh complete 

 also (Fig. 20). 



The smallest of these forms (Fig. 24) is 19 mm. high with a relatively deep calice, 

 and attached by the side of its stalk. From a comparison with the instars of Fungia, 

 which I collected myself, I am inclined to believe that it is rather an anthoblast than a 

 trophozooid. In all the rest at the top of the stalk immediately under the horizontal 

 anthocyathus there is a distinct pitted ring (Fig. 21 b), where the break would ultimately 

 have taken place. Above this the corallum is white anil translucent while below it is 

 dark and opaque, showing that it is to some extent changed. The part between this 

 and the top ring is in no case overgrown by organisms, and it seems to be probable 

 that the body-wall of the polyp formerly covered it. The detachment of the 

 anthocyathus would seem, indeed, to be effected in precisely the same way as Bourne 

 has described for Fungia. The costae vary, in some being almost smooth ridges and 

 in others having the adult characters. 



The smallest free anthocyathus is slightly oval in shape, 20 mm. by 17 mm. in 

 diameter (Fig. 19). On the aboral surface the scar is well marked, but the opening from 

 the exterior into the coelenteron has been closed by corallum, owing apparently to 

 thickenings of the sides of the septa. A slightly larger but irregular form, 23 mm. 

 in greatest diameter, has the opening still complete (Fig. 18). The broken edges of the 

 septa have an extremely opaque, white colour ; and above them the septa and trabecula 

 of the columella appear to have been thickening so as completely to close in the 

 coelenteron. The scar is somewhat oval, 6'5 by 5 mm. in diameter, and in it the 



