No. 426.] MADREPORARIAN CORALS. 467 
The six septa were free from one another and from the epitheca, 
and situated at equal distances apart within the primary ento- 
coelic chambers, thus alternating with the cycle of six exoccelic 
tentacles first to arise. 
A day or two after the formation of the first cycle of ento- 
septa the six exoccelic septa began to make their appearance, 
in some cases simultaneously, but successively in others, in 
bilateral pairs from the dorsal to the ventral aspect of the polyp. 
Under ordinary transmitted light no basal skeletal formation 
could be detected, but with polarized light the presence of 
crystalline particles could be demonstrated. In polyps macer- 
ated at this period a very thin basal disk was recognizable, 

Fic. 3. 
formed of an aggregation of irregular granules, and continued 
at its edge as the upturned epitheca, the six or more radial 
septa arising from it vertically some distance within. 
A wide range of variation was exhibited by the different 
polyps as to the rate of growth of the various organs, especially 
in the later stages. The individuals which were larger on fixa- 
tion soon outstripped the others; scarcely any succumbed, 
and it was possible to feed them on fragments of worms and 
mollusks. 
Such a regular, symmetrical development was characteristic 
only of the isolated polyps, free to expand equally on all sides. 
The polyps in groups were crowded to such a degree as to 
necessitate arranging themselves at all angles with regard to 
one another and the incrusted object. Sometimes part of the 
base of one polyp would be reclining against part of another ; 
but none of the individuals seemed to be overpowered by such 
