78 OLWEN M. EEES. 



zooxanthellse. There is a definite nerve layer at the base of the 

 ectoderm in the region around the tip where there are numerous 

 nematocysts to control. The mesogloea is dense, but becomes more 

 fibrillar towards the base, where it also sends out branches which 

 very often divide. Near the base also the nerve layer becomes much 

 thinner. 



Septostomes or Mesenterial Stomata. 

 " In the genus Actinia these stomata are found in the uppermost inner 

 angles of the complete mesenteries close beneath the mouth, and are 

 probably the result of incomplete union of the mesentery with the 

 stomatodseum." This is how they are described by Professor Bourne in 

 (5). They are known as internal stom^ata. In some other Actiniae, 

 e.g. Tealia coriacea (crassicornis) and Metridium dianthus, external 

 stomata are present. These are openings situated in the upper third of 

 each mesentery between the longitudinal and the parietal muscles. 

 In Metridium septostomes are found on many of the imperfect as well 

 as on the perfect mesenteries, though there are no septostomes on the 

 directive mesenteries. Both internal and external septostomes are 

 present in some anemones, e.g. Hertwig says of the Actinian which he 

 named Dysactis crassicornis, " Two kinds of stomata are found on the 

 muscular part of the septa — the peristomial or external stomata are 

 very large, whilst the marginal which lie close to the wall are small." 

 These septostomes are also found in the primitive anemones, e.g. Hal- 

 campa clirysanthellum possesses external stomata. No septostomes 

 were found in any of the Edwardsidse. External stomata are present 

 in all the mesenteries of Eloactis mazeli, and each takes the form of an 

 elongated slit down the mesentery separating the retractor muscle from 

 the parietal muscle. These stomata provide a means of communication 

 between the radial chambers separating the mesenteries, and probably 

 thus ensure a better method of circulation. Again, undoubtedly they 

 facilitate rapid retraction, for without the septostomes there would be 

 a danger of the mucilage, etc., present in the radial chambers of the 

 coelenteron getting clogged in the uppermost parts, whereas the presence 

 of the septostomes provides free passage from one chamber to another, 

 not only by way of the axial space into which they all open, but also 

 via these stomata. 



Systematic Position of Eloactis mazeli. 

 Delage and Herouard (6) have temporarily placed this anemone in 



