226 CEYLON PEARL OYSTEE REPORT. 



various shape, two of which are shown in fig. 20. They were very abundant in one 

 series, but entirely absent in another, and in a third they were rare. They are filled 

 with large refracting granules, which generally stain crimson in picro-indigo-carmine, 

 but in some cases they stain a deep indigo blue. They can be nothing else than 

 amoebocytes. and are probably excretory in function. Their abundance in one 

 specimen and their rarity or absence in others is probably attributable to the different 

 conditions of nutrition of the polyps in question. It is well known that the 

 endodenn of Ccelenterates, e.g., of Hydra, presents very different appearances 

 according as the animal has been recently fed or starved, and I have found the most 

 diverse appearances, particularly in the matter of the presence or absence of 

 endoderm cells loaded with granules, in the endoderm of Hydra, according as they 

 had been fed abundantly or starved. 



Finally, it may be noted that at the bottom of the axial cavity there are large 

 spaces, and frequently there is a single large central space in the axial gastro- 

 vascular cavity. The endoderm lining these spaces or space is invariably devoid of 

 Zooxanthellse and gland cells, and has the simple columnar form depicted in fig. 21. 



As regards the occurrence of nematocysts in the endoderm, I occasionally found 

 large nematocysts, of the second type characteristic of the tentacular batteries, in 

 the tentacular endoderm, but invariably in close proximity to one of the batteries. 

 I conclude, therefore, that these nematocysts were not formed in the endoderm, but 

 have been forced through the mesoglcea into the endoderm during the violent 

 contraction produced by the action of reagents. Elsewhere I could find no trace of 

 nematocysts of any kind in the endoderm. 



2. Heteropsammia michelini, M. Edw. and H. 

 (Plate IV., figs. 22 to 25.) 



The remarkable analogies between this coral and Heterocyathus CBquicostatus have 

 been commented on by several authors. Both are built up round a gastropod shell 

 tenanted by an Aspidosiphon, both have an exactly similar spiral Aspidosiphon 

 chamber in the adult state. In both there is a minute Lamellibrauch commensal 

 with the Aspidosiphon within the chamber, and in both there is a number of minute 

 tubes lined by ectoderm leading from the lateral walls of the coral into the chamber 

 in question. The shape and general appearance of the two corals is closely similar, 

 but whereas Heterocyathus is always a simple coral, Heteropsammia michelini 

 generally exhibits two calices produced by fission of the parent calicle, and H. multi- 

 lobata exhibits several calicles. The anatomy of the last-named species has been 

 described by Fowler (18), who notes the following features. The external soft 

 tissues rest on the echinulations of the cienenchyme ; the tentacles are simple, without 

 nt'inatocyst batteries, and are apparently both exoccelic and endocoelic ; exosepta and 

 endosepta are present, and certain of the septa fuse centrally, as in Rliodopsammia 



