216 Mr. J. E. Duerden on the Genus Alicia. 



then, as it is the type of its genus, it will retain tlie name 

 Alicia, and A. costa', Pane., will be referred to its original 

 genus Cladactis, with the definition given above. 



Alicia costce, Pane. 



The description of the external characters is sufficiently 

 well given by Andres, who also devotes a beautiful plate to 

 the species. The following details refer only to the histo- 

 logical features. 



Column. — The column is thin and delicate, somewhat 

 thicker in the region of the sphincter muscle, but very thin in 

 the vesicular region. The ectoderm is regular and covered 

 on the outside with a delicate cuticle. The sphincter region 

 of the ectoderm is crowded with elongated nematocysts, 

 showing very distinctly the internal spiral thread ; somewhat 

 above and below this region the nematocysts are arranged in 

 groups, as in the tentacles. In the vesicular region the 

 ectoderm is much thinner and nematocysts are rare. 



The mesogloea varies in thickness, as does the ectoderm. 

 It is homogeneous in structure, except for the presence of a 

 few minute cells. 



The endoderm is very thin throughout and shows a weak 

 endodermal muscle. 



Vesicles (PI. IX. fig. 2). — The stem or peduncle of the 

 vesicle shows a regular ectoderm with a thin cuticle, but 

 without any nematocysts; the mesogloea is thicker than that 

 of the enlarged portions, and tJie endoderm forms a weak 

 basal muscle. The distal portions of the vesicles possess a 

 thicker ectoderm, with a few nematocysts. The ectoderm 

 seems largely made up of elongated unicellular glands, which 

 stain deeply. It is pmbabie that the vesicles are partly glan- 

 dular in function. They are not batteries of nematocysts. 

 The mesoglo3a is very thin, and the endoderm contains 

 markedly the pigment granules which give the bright colo- 

 ration to the vesicles in the living animal. 



Tentacles (PL IX. fig. 3). — The walls of the tentacles are 

 very thin, with small batteries of nematocysts arranged at 

 intervals all over the surface. The nematocysts are large, elon- 

 gated, and show the spiral thread distinctly. Accompanying 

 them are deeply staining unicellular glands. The mesogloea 

 appears only linear in section. The endoderm is about half 

 the thickness of the ectoderm and evenly arranged. A very 

 weak ectodermal muscle can be distinguished in transverse 

 sections and an endodermal one in longitudinal sections. 



Dis]{. — In the disk the ectoderm is very thick and shows 



