436 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



A gonidial groove at each end of the stomodseum is, w ith certain exceptions, present in all 

 Hexactinise; and a single groove occurs in the Zoanthese and Cerianthese. In the Zoantbeaj the 

 organ is ventral or posterior, while, according to Carlgren (1893, p. 243), it is dorsal or anterior 

 in the Cerianthese. A ventral groove, first termed by Professor Hickson (1883) the Siphonoglyphe, 

 is likewise found in nearly all Alcyonaria. It is, therefore, a little remarkable to find that such a 

 typically Anthozoan organ has never been established for the Madreporaria, and it is absent from 

 each of the twenty-six species here studied . Its non-development is probably indicative of 

 the more primitive character of coral polyps generally compared with most Actiniaria. 



The suggestion may be offered that the grooves, already described as occurring all the way 

 round the stomodamm in some species of Madreporaria, are to be regarded as the "morphological 

 and physiological equivalents of the two axial grooves in the Hexactinian polyps. Instead of 

 a groove occurring only between each pair of directives, one is found between all the complete 

 mesenteries. The same histological differences are found in each case, though not so pronounced 

 in corals. No experiments have been made to determine whether the grooves in the Madre- 

 poraria have any special function in directing the inhalent and exhalent currents, and with such 

 small oral apertures experiments of this character would be difficult to conduct. 



In living polyps of Cladocora arbuscula, Solmastrsea hyades, and others, the lateral por- 

 tions of the lips and stomoda?al walls have at times been observed to come into close contact, 

 leaving a small aperture at each extremity of the mouth, through which currents of water enter 

 or leave the gastric cavity. A similar approximation has also been recorded by different 

 observers as occurring among the Actiniae, but is there associated with the presence of gonidial 

 grooves. In the Zoanthida?, provided with only one gonidial groove, only one terminal aperture 

 remains when the lips are approximated. 



The inner stomodseal extremity may become reflected upwardly and outwardly, so that in 

 transverse sections the stomoda j al walls are cut through twice; or, if they are much folded in 

 addition, they may appear several times in succession in the same section. The appearance of 

 the reflection in longitudinal section is shown on PI. VII, fig. 5(1. and in transverse section on 

 PI. VI, fig. 51. The stomodamm terminates internally at practically the same level all the way 

 round, or the two axial extremities, with the. directives attached, may extend a little below the 

 lateral walls, but nothing comparable with the " Languettes'" of Actinians has been observed. 



Upon complete retraction of the polyp, the distal parts of the polvpal tissues — upper column 

 wall and disk — mostly come to rest upon the skeletal projections — septa, pali, columella; in 

 consequence of which the stomodseum becomes flattened and more or less irregularly folded. 

 As a result it is often with difficulty that transverse sections of the stomodseum, exhibiting the 

 relations of the mesenteries, can be obtained, especially as the organ is comparatively short. 



On retraction the stomodseal walls as a whole are sometimes thrown into a few deep vertical 

 folds, which assume a symmetrical figure. This is especially the case in Pwites (tigs. 28, 30); the 

 folds may be four or six in number, and approach so as to touch one another in the middle, 

 practically obliterating the lumen. The stomodseal foldings of a bud of Cladocora likewise 

 assumed a regular arrangement (PI. VIII, fig. 60); Fowler (1888) also describes and figures a 

 similar appearance in a transverse section of the stomodseum of Seriatopora svblata. No doubt 

 it is a consequence of the strong contraction of the circular endodermal muscle. 



The histological details of the stomodseal wall are practically alike in all Madreporarian 

 polyps, and agree closely with those of the Actiniaria. The ectoderm is always a broad, strongly 

 ciliated layer, comprised largely of supporting veils, the nuclei of which are closely arranged, 

 and give rise in sections to a characteristic, brightly-staining zone. The ciliation is uniform 

 throughout, and is nearly always persistent in preserved material. As a rule nematocysts of 

 two or three kinds occur, while both clear and granular gland cells are numerous. The latter 

 are particularly abundant in Gladocora (tig. 525). In some cases, e. g., Phyllangia, distinct 

 ectodermal nervous and muscular (dements can be made out near the mesoglceal surface, but are 



"Saville Kent refers to a siphonoglyp in a Barrier Reef Fungia, and Bourne adds one to his diagrammatic figure 

 of a coral, en p. 62 of His article Anthozoa i 1900). 



