ON THE POSTEMBRYONIC DEVELOPMENT OF CYCLOSERIS. 173 



is straight and incrusted by a Polyzoon right up to the edge of the calice, which 

 is accordingly bent slightly inwards. There are seven septa at nearly equal distances 

 from one another round the calice, but six are subequal, broad, thick and covered 

 with rough spines while the seventh is comparatively narrow and smooth ; the former 

 are termed throughout the primaries. In the centre of the calice is a single 

 prominent, rough papilla — the columella. 



The next two instars are also attached to the aboral surface of the same dead 

 anthocyathus. The second is about 07 mm. in diameter by 0'5 mm. high, and was 

 apparently covered up to the edge of the calice by an incrusting sponge, which grew 

 to some extent over its opening. The septa are difficult to distinguish, but ten or 

 eleven seem to be present, some of which are very narrow and rudimentary; the 

 columella is deeper and less prominent than in the preceding instar. Attached close 

 to the base of this form is another trophozooid of almost the same size, which has 

 been completely killed by the same sponge; it appears to have ten septa, subequal 

 in size. 



The third instar (Fig. 11) is straight, about 12 mm. in diameter by - 7 mm. in 

 height. Fourteen septa are present, which cannot however be distinguished into cycles. 

 Two are extremely thin and rudimentary, while four others do not appear to fuse with 

 the rest in the centre of the calice; the remainder vary in thickness and are slightly 

 exsert with rough granular spines. The axial fossa is deep, about 0'4 mm. broad and 

 closed in below by the fused septal brabeculae from which project three large, rough 

 papillae, one of which lies almost centrally, and is, I believe, the true columella. 

 The wall is covered on the outside by an incrusting alga ; it appears to be in 

 some places double and to consist of a fused theca and epitheca. 



The above forms are, I believe, true trophozooids, directly developed from the 

 ovum. In many of the succeeding instars it is impossible to see whether the young 

 form has been developed from a trophozooid, an anthoblast (if such exist), or by the 

 re-growth of an anthocaulus. The development of the skeletal parts appears to 

 follow along the same lines so that I shall briefly describe them, mentioning to 

 which category each form seems to belong. 



The next instar (Fig. 12) has 28 septa. It is the re-growth of a nearly straight 

 anthocaulus from which three anthocyathi — the lower two represented by rings— appear 

 to have separated at the heights of 4, 6-5 and 8 mm. above its attached base. The 

 anthocaulus where the last anthocyathus separated is about 35 mm. in diameter while 

 the young anthocyathus is still straight, about 1 mm. high by 2 mm. in diameter. The 

 six primary septa can be clearly distinguished, being thicker, more spinulose and 

 markedly broader than the rest. The remainder vary considerably, one of the secondaries 

 being almost as thick and exsert as the primaries, but clearly joined at its sides by 

 two of the tertiaries. The axial fossa is large and closed in below by a trabecular 

 columella, with which most of the septa appear connected. 



The commencement of the horizontal growth is clearly seen in another specimen 

 (Fig. 13), formed by the re-growth of an anthocaulus, from which one anthocyathus has 

 separated. The calice is about 7 mm. in diameter while the stem is 35 mm. Four 

 cycles of septa are complete and there are also 8 septa of the fifth cycle. The primaries 

 are quite distinct while the quaternaries are fused to the tertiaries, which are 



