20 G. HERBERT FOWLER. 



the Perforata, and Stylophora (7), Seriatopora and Pocillopora 

 (described below) among the Imperforata, are the recorded instances, 

 all possessing well-developed coenenchyme. 



In a minor point only do my observations differ from those of 

 von Koch (7), viz., that he figures no mesoglcea between the echinu- 

 lations and the ectoderm ; in other words, according to his figure 

 the persistent ectoderm of the body wall is at those points continuous 

 with the calycoblast layer (Fig. 5). The reason which leads me to 

 believe in the existence of a mesoglcea lamina between calycoblasts 

 and external ectoderm, is that at the points where through shrinkage 

 the echinulations have pierced the external body wall, they have 

 carried with them this mesoglcea, which in sections of decalcified 

 specimens preserves accurately their outline, projecting far beyond 

 the shrunken ectoderm. 



Between this external body wall and the corallum lies the system 

 of approximately longitudinal canals with transverse commissures ; 

 in other words, the space between the body wall and the theca is 

 broken up into canals by the points of contact. These canals com- 

 municate, as is usual in Perforata, with the canals which permeate 

 the corallum and run also into the polyp cavities. 



The polyps are built on the normal Actinian type. As the calyces 

 are placed only on the inner side and on the lip of the crateriform 

 colony, an easy identification of bilaterality is thus afforded, the 

 dividing plane being a radius directed to the centre of the goblet. 

 Approximately at the ends of this dividing plane are placed the 

 axial and abaxial pairs of "directive " mesenteries, distinguished by 

 the arrangement of retractor muscles on their ectoccelic faces. The 

 polyps are not, however, rigidly bisymmetrical, inasmuch as the 

 pairs of mesenteries lying right and left of the dividing plane are 

 not equal in number. 



The total number of pairs of mesenteries is not constant, but does 

 not appear to depend upon the size (age) of the particular polyp. 

 It varies generally from 17 to 22. The asymmetry of the polyps 

 can best be seen in a tabular form : — 



ABC 



Number of pairs of mesenteries 17 20 22 



Number on right side of "directives"... 7 10 9 



Number on left side of " directives " ... 8 8 11 



