SEA ANEMONE. 



241 



the exception of the ' directive septa ' (infra) the surface turned towards the intra- 

 septal chamber a more or less pronounced ridge may be seen traversing it 

 from peristome to base. This ridge indicates the position of the retractor or 

 tentacular muscle of the peristome. In the case of two pairs of primary mesenteries 

 (in the strict sense) this muscle runs on the inter-septal surface. The two pairs 

 in question correspond one to each oral angle, and are known as 'directive septa.' 

 They divide the animal into a right and left half, and extend downwards along 

 the lappets of the oesophageal groove. 



The innermost circle of tentacles is the oldest. There are in a few instances 

 circum-oral and intermediate tentacles, i. e. tentacles placed round the mouth and 

 between the mouth and marginal tentacles respectively. 



The marginal sphincter muscle is rarely completely absent as in Corallimor- 

 phus, but the degree of its development varies very much. In Tealia it is 

 remarkably strong. 



The mesenterial filament which borders the free edge of each mesentery 

 consists typically of three processes one median covered with thread-cells and 

 gland cells, and one on either side of the median with ciliated cells. The two 

 lateral processes are present at the peristomeal end of the mesentery while they 

 die out gradually towards its basal end. 



In some forms, e. g. Sagartia, there are long vermiform mobile filaments 

 attached to the surfaces of the mesenteries close to the basal end of some of the 

 mesenterial filaments. These threads are the acontia. They can be protruded 

 from the mouth or from a series of apertures the cinclides near the base of the 

 animal. One surface of an acontium is loaded with many thread-cells. The cyiclides 

 are certainly in some cases, e. g. Sagartia, Adamsia, genuine preformed apertures. 

 It is not certain however that accidental ruptures of the wall may not take place 

 occasionally. 



Tealia and some other forms have the sexes separate. The male and female 

 elements are alike derived from the endoderm. They occur only on the tertiary 

 mesenteries or mesenteries of a lower order. They are situated between the 

 mesenterial filament and the tentacular muscle. Many Sea-Anemones produce 

 living young, resembling in shape the parent form. 



It has been proved that some Anemones possess the power of multiplying by 

 ' scissiparity/ A small portion of the limbus grows and separates itself from the 

 parent, taking away a part of at least four mesenteries. 



The tissues present in Tealia are an ectoderm, a supporting lamina or meso- 

 dermic layer, and an endoderm. The latter clothes the whole coelenteric space, 

 central and peripheral, including its extension into the tentacles. 



The ectoderm consists of (i) ciliated cells, with flat triangular bases ; (ii) 

 gland cells ; (iii) sense-cells which end internally in fine filaments connected to a 

 nervous plexus ; (iv) cells containing thread-cells or nematocysts, perhaps similarly 

 connected ; (v) muscle and ganglion cells placed sub-epithelially. Both (iii) and 

 (iv) are provided with a fine tactile bristle. The muscle- and ganglion-cells 

 lie next to, or are actually imbedded in, the supporting lamina, the latter especially 

 in the peristome. The ectoderm is unilaminar in the wall, base, and stomodaeum. 

 In none of them does it possess muscle-cells ; and in the two former no ganglion 

 cells. The mesodermic layer or supporting lamina is laminated ; is thickest in the 



R 



