422 G. HERBERT FOWLER. 



it is placed by Martin Duncan ( f Journ. Linn. Soc./ xvii). From 

 the latter it differs, in that soft tissues are present on the 

 outside of the theca. The septa are both ectocoelic and 

 entoccelic, and to both sets correspond true costse, which 

 extend downwards for some distance over the external surface 

 of the corallum. 



As was suggested by Moseley (" Chall." Rep. Zool., ii, p. 159), 

 in complete retraction the tentacles are covered over by the 

 mouth-disc, which is drawn inwards by a stroug sphincter 

 muscle (fig. 9). This constitutes the first recorded occurrence 

 of "Rotteken's muscle'' among Madreporaria; in longitudinal 

 section it has the same " diffuse" appearance as that figured by 

 theBrothers Hertwig,in S agartia parasitica ('Jen. Zeitschr./ 

 xiii, pi. xix, fig. 18.) The mouth-disc itself is much corru- 

 gated, the rugse consisting of lengthened columnar ectoderm 

 cells supported by solid outgrowths of the mesogloea, which 

 is at this point very thick (fig. 10, a). The ectoderm of the 

 tentacles consists almost entirely of nematocysts, showing 

 but slight arrangement into batteries. The tentacles are ap- 

 parently entoccelic only. The mesenteries appear to be 

 normal, but in the fragment used for microscopic sections no 

 directives were present. Both retractor (longitudinal) and 

 protractor (oblique) muscles are exceptionally well developed, 

 the former applied to such arborescent pleatings of mesogloea as 

 have been described among both Madreporaria and Hexactinise. 

 It is worthy of note that there is so little cohesion between the 

 muscle-fibres and the mesogloea which affords them support, 

 that they are frequently seen in transverse sections to tear 

 away with the endoderm, leaving the mesogloea bare. Over 

 the whole of the polyp the mesogloea is unusually strongly 

 developed, and it exhibits at some points, the position of which 

 appears to imply a more recent secretion than elsewhere, a 

 great affinity for carmine, and a markedly vacuolated structure. 

 The vacuoles are often empty, but contain, in many cases, 

 brilliantly refractive crystals, the nature of which I was unable 

 to ascertain. Cells are rarely to be seen in the mesogloea. 

 The processes for attachment of the mesentery to the corallum 



