ZOOLOGY OF THE BEEMUDAS. 107 



the column, and is almost covered by the infolding of the column 

 walls over it; this apparently, however, is an abnormal condi- 

 tion. The column is smooth, and no traces of cinclides could 

 be seen as stated above. Seclions (PI. 10, fig. 2) show that 

 the mesogloea is thin throughout, and that the circular muscles 

 (cm) are only feebly developed. There is a special sphincter 

 (sp) imbedded in the mesogloea, immediately below the margin, 

 and, though not very powerful, is yet quite apparent. The 

 only species of Aiptasia in which such a sphincter has been ob- 

 served as yet is A. pallida of OUT Eastern coast. Immediately 

 below this the mesogloeal muscular processes which support 

 the circular muscles are weak, but further down they enlarge 

 gradually and form a second sphincter (sp') similar to what 

 has been described by R. Hertwig* in Ldotealia nymphoea. It 

 is to the presence of this lower sphincter that the contraction 

 of the column mentioned above is due. 



The tentacles are 48 in number and are arranged in four 

 cycles. They are strongly entacm8eous,.and are not infolded 

 during contraction. Those of the first cycle measure 1.1 cm., 

 and those of the outermost cycle 0.3 cm. The ectodermal and 

 endodermal muscular processes are present, but do not call for 

 a special description. The disc is flat and the stomatodseum is 

 without well-marked gonidial angles; sections show that the 

 grooves are hardly developed. 



The mesenteries are in four cycles. The six pairs of the first 

 cycle are alone perfect ; those of the second cycle are shorter 

 but provided with well-developed longitudinal muscles, while 

 neither those of the third nor those of the fourth cycle 

 have the longitudinal muscles, the members of the latter cycle 

 not projecting above the surface of the endoderm. The parieto- 

 basilar muscles seem to be wanting, or at least have no marked 

 mesogloeal processes. The reproductive organs are borne by the 

 mesenteries of the second cycle, and also by those of the first 

 cycle (except by the directives) below the internal opening of 



*R. Hertwig — Report on the Actiniaria. Zoology of the Voyage of H. M. S. 

 Challenger. Vol. vi. Pt xv. 1882. 



