MATTHAI— RECENT COLONIAL ASTR^IDiE 21 



chambers; following Fowler's terminology those from the entocoeles are known as " entocoelic 

 tentacles " (" tentacules loculaires " of Faurot) and those from the exocoeles as " exocoelic 

 tentacles " ("tentacules interloculaires" of Faurot). They do not always agree in numbers 

 with those of the entocceles and of the exocoeles. In the retracted condition of the polyps, 

 I have not been able to make out more than two cycles — an inner and an outer — the 

 former being composed of the entocoelic tentacles, and the latter of the exocoelic tentacles. 

 The term "cycle"* refers to those tentacles which form a circle, i.e. which arise from 

 about the same radial distance from the mouth. In some species one of the two cycles is 

 absent. When the polyps are retracted, the tentacles are usually bent over the oral-disc, 

 so that, in transverse section, they are cut longitudinally ; they are also capable of 

 complete introversion, i.e. of being turned outside in. A tentacle can be distinguished, 

 from any mere fold of the peristomial wall, by the swellings caused by the presence 

 in its ectoderm of batteries of nematocysts. 



A large terminal battery is always present which makes the tentacular tip knobbed 

 or bluntly pointed ; such a battery consists of a peripheral row of closely arranged type I 

 nematocysts with II & ones interspersed among them. Much smaller subterminal batteries 

 are present in most of the polyps ; the number constituting a longitudinal row is of 

 specific value. In these batteries only type I nematocysts are present ; they spread 

 outwards towards the periphery, hence their arrangement in each battery appears fan- 

 shaped in transverse section. Nuclei are numerous below the peripheral row of 

 nematocysts; those towards the mesogleea are round and homogeneously stained, while 

 those towards the nematocysts are elongated, saccular and granular. There are no 

 diverging tracts of protoplasm as in the oral-disc and edge-zone, but like the latter 

 filamentar processes (neuro-muscular) pass from the nuclei towards the mesoglsea. 

 As described on p. 17, a longitudinal muscular layer and a granular nervous layer are 

 pi'esent. 



The endoderm varies considerably in thickness from being extremely thin to being so 

 thick as almost to occlude the lumina of the tentacles. 



Stomodseum (Plates 7 — 10). Van Beneden in 1898 questioned the use of terms like 

 stomach, pharynx, oesophagus to denote the tubular structure of the Anthozoa. He 

 objected also to the use of "stomoda3um" on the ground that the organ in question is 

 not homologous with the stomodseum of the higher Metazoa. In like manner, he held 

 that any general use of the word " mouth " would lead to confusion. Both terms are 

 here retained without having recourse to new names like "Actinopharynx " and "Actino- 

 stome." On the other hand, van Beneden's " enterostome " is a much needed name to 

 denote the lower opening of the stomodaeum into the gastro-vascular cavity or coelenteron. 



The stomodseum (" stomatodaeum " of Fowler and McMurrich) in coral polyps 

 is usually flattened from side to side in common with most of the Anthozoa, rarely 

 being circular in transverse section. The mouth in many polyps forms a more or less 



* Faurot (40, p. 58), uses "cycle" in practically the same sense, i.e. to denote the rings of tentacles, 

 and " order " when referring to the sequence of the circles of mesenteries. According to him, in Actinians, the 

 exocoelic tentacles, which are smaller than the entocoelic ones, . constitute the last cycle but are formed at 

 successive periods in the exocoeles, following the appearance of the orders of mesenteries. 



