1889.] NATURAL SCIENCES OF PHILADELPHIA. 103 



umn each specimen presents a well-marked constriction, below which 

 the column is cylindrical, while above it it gradually expands, the 

 disc not being; at all infolded in contraction. The base is 

 evidently adherent, but in two of the specimens it is much 

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

 the column walls over it ; this apparently, however, is an abnormal 

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

 be seen as stated above. Sections (PI. VI, fig. 2) show that the mes- 

 ogloea 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 observed as yet is A. pallida of 

 our Eastern coast. Immediately below this the mesoglceal muscular 

 processes which support the circular muscles are weak, but further 

 down they enlarge gradually and form a second sphincter (sp 1 ) sim- 

 ilar to what has been described by R. Hertwig 1 in Leiotealia nym- 

 phcea. It is to the presence of this lower sphincter that the con- 

 traction of the column mentioned above is due. 



The tentacles are 48 in number and are arranged in four cycles. 

 They are strongly entacma?ous, and are not infolded during contrac- 

 tion. Those of the first cycle measure 1.1 cm, and those of the outer- 

 most 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 stomatodaeum 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 and 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 sur- 

 face of the endoderm. The parieto-basilar muscles seem to be want- 

 ing, or at least have no marked mesogloeal processes. The repro- 

 ductive organs are borne by the mesenteries of the second cycle, and 

 also by those of the first cycle (except the directives) below the in- 

 ternal opening of the stomatoda?um. This is the only Sagartid, with 

 the exception of A. pallida, in which I have observed reproductive 

 organs on the mesenteries of the first cycle, and it is a case of con- 



1 A'. Htrtwig — Report on the Actiniaria. Zoology of the voyage of H. M. S. 

 Challenger. Vol. vi. Pt. xv, 1882. 



