642 me. j. e. dueedelsr 01^ the relations of 



Lips, Stomod^um, and Gtonidial Grooves. 



In most Actiniaria no very sharp line o£ demarcation between 

 the disc and stomodseal walls is observable ; the lips are 

 tbickeced, and the transition from the external to the internal 

 tissues is gradual. The same may be aflS.rmed of the strong 

 histological alteration which is always presented between the 

 ectoderm of the disc and that of the actual stomodseum. In 

 many Madreporaria, especially in those forms where numerous 

 oral apertures are enclosed within one system of tentacles, the 

 distinction between the coloured disc and the white stomodseum 

 is very clearly and sharply defined by a definite border. Amongst 

 .anemones Micordea and Mhodactis are the only examples in 

 which, in my experience, such a sharp boundary can be ob- 

 rserved; the peristome is elevated, but no rounded lips serve 

 as a means of gradual transition from the exterior to the 

 interior. 



Eurther, the stomodseal wall in all Actinians may be thrown 

 into longitudinal ridges and furrows, more marked in contracted 

 preserved specimens. They are, however, rarely regular or 

 permanent and, with the exception of those due to the attach- 

 ment of the mesenteries, are not recognizable in the living 

 extended polyps. In the two genera just mentioned the outer 

 ^Esophageal surface throughout its whole extent displays deep, 

 sharply-defined corrugations, which do not disappear when the 

 mouth is fully extended or the oesophagus partly protruding. In 

 microscopic sections the ectodermal ridges are seen to be supported 

 upon very considerable processes of the mesoglcea, greater than 

 those which occur in other anemones. They bear no definite 

 relation to the number and position of attachment of the 

 mesenteries connected with the wall internally. McMurrich 

 (1889) in his description of the two "West-Indian species, also 

 mentions these pronounced folds, and figures (pi. iv. fig. 3) the 

 appearance presented in transverse sections by those of Bhodactis 

 Sancti- ThomcB. 



The stomodaeum of most of the corals I have examined exhibits 

 a similar appearance. "When the mouth is opened and the stomo- 

 dseum partly extruded of such a form as Manicina, regular distinct 

 white ridges are displayed all along the length of the latter, the 

 number being about eight on each side, but varying with the size 



