the Actintarian Family Aliciidaj. 9 



latter layer is very thin. Tlie encloderm is narrow and 

 contains zooxantliellai. 



In several specimens sectionized the endoderm is divisible 

 into two portions — a proximal, which is largely reticuhir in 

 character, and a more internal part crowded with nuclei and 

 zooxantlielloe (figs. 3, 4). The separation of this reticular 

 layer, sometimes on the endodermal side and sometimes on 

 the ectodermal side of the mesogloea, is a well-marked feature 

 of some examples and is found practically throughout the 

 wliole polyp. The reticulum appears to be formed of the 

 nervous and perhaps muscuhir and mesogloeal elements, 

 probably separated more distinctly by the unequal contraction 

 of the mesogloea and the two other layers, but is not a con- 

 stant feature of the species, being evidently partly dependent 

 upon the method of preservation. In vertical sections of the 

 base the mesogloea borders directly on the ectoderm, and the 

 reticulum is on the endodermal side, whereas in the tentacles 

 it is on the ectodermal side. 



Column-wall. — The column-wall is very delicate and much 

 broken up below by the outgrowths forming the vesicles. 

 The nuclei in the ectoderm are uniformly distributed ; nemato- 

 cysts apparently do not occur, except a few, similar to those 

 of the tentacles, in the capitulum. An ectodermal muscle on 

 small mesogloeal plaitings can be distinguished. The meso- 

 gloea is thicker tlian at the base and contains a few isolated 

 cells. The endoderm has abundant nuclei and zooxanthellae. 

 The vesicles are hollow outgrowths of the body-wall, but; 

 their structure differs somewhat. The thickenings and 

 tubercles seen externally are shown in sections to be batteries 

 of nematocysts. The stinging-cells are very long, extending 

 across the ectoderm, and are limited to the enlarged areas. 

 Many cysts present a fine internal beaded character, due to the 

 spiral thread seen in optical section, while others, mostly in 

 the deeper parts, show no thread and may have the contents 

 staining deeply, being evidently only in process of development. 

 Small oval nuclei are, more particularly in the thickened 

 regions, arranged in a narrow belt just below the surface. 

 The remaining area is much vacuolated in places. The ecto- 

 derm of the vesicles where devoid of nematocysts is very thin. 

 The mesogloea is narrow. The endoderm contains zooxan- 

 thellse, but not pigment granules such as are abundant in ^ . costce 

 and A. mirahilis. A slight endodermal muscle can be distin- 

 guished. In the difference in the characters of the nemato- 

 cysts in the vesicles and those of the column-wall and tentacles 

 Bunodeopsis agrees with the two species of Alicia examined. 

 They are, however, larger in the latter genus. 



/Sphincter muscle. — The sphincter muscle is of the diffuse 



