HEX ACTINIA FKOM NEW SOUTH WALES. 41 



touch. The suckers are fewer and smaller in the contracted physa, which is 

 covered by deeper ectoderm and presents a smoother external surface. The 

 border of the ectoderm is thickly set with long oval nematocysts, lying at right 

 angles to the surface (PI. 4. fig. 5, nem.). These are most numerous in the 

 capitulum and upper scapus^ where they form a continuous border touching 

 one another. The large glandular cells recognized by Faurot in Peaclda 

 hastata (15) are not distinguishable, probably owing to the state of pre- 

 servation. The ectoderm cells are very long and contain rounded nuclei, 

 internal to which lies the clear, slightly granulated, nervous layer. I have 

 not been able to detect ectodermal muscle in my preparations. The mesogloea 

 contains many isolated cells, and is laminated throughout the polyp, this 

 lamination being most marked in the column-wall, where the laminae are so 

 thin as to give the whole structure a fibrous appearance. 



The endodermal muscle system is strong and strengthened locally in both 

 capitulum and lower scapus. The plaitings of the mesoglcea, on which the 

 muscle-cells are placed, line the capitulum and scapus throughout, and are 

 present in the greater part of the physa also. These mesogloeal plaitings all 

 contain a darker-staining centre core, surrounded by lighter-coloured sup- 

 porting substance. In the capitulum and thiough the greater length of the 

 scapus they are simple and, in longitudinal sections, have the appearance of 

 a band of narrow wavy ribbon running down the column between the mesoglcea 

 and endoderm. In the lower scapus they become branched and finally assume 

 a dendriform appearance, reaching their maximum strength in the scapus 

 adjacent to the physa, where they form long tongues stretching into the 

 coelenteron. On each side of these tongues are branches, which often divide 

 again, thus largely increasing the surface (PL 4. fig. 5). Between these 

 dendriform structures shorter projections are present. This is the strongest 

 part of the body-wall, and it is these muscles, probably, wdiich enable the 

 animal to bore into the sand with its physa and to bury itself up to 

 the capitulum. Holdsworth (3) and Faurot (15) have carefully described 

 this process in the case of Peacliia hastata, and estimated the time taken in 

 boring at about an hour ; but the endodermal muscles present in the scapus 

 of any species of Peacliia have not hitherto been described. 



The endoderm of the column consists of long narrow cells, which are very 

 easily separated from one another. The endoderm is narrow in the upper 

 part of the polyp, but becomes extremely thick in parts of the physa, as 

 does the ectoderm also. It is, however, probable that the physa is much 

 contracted. 



The Sphincter. — The sphincter is represented in Peachia hilli by an increase 

 in strength of the endodermal muscle plaitings present in the capitular 

 region. The plaitings remain simple and are still very small, but are never- 

 theless about twice the length of those present in the upper scapus. 



Disc and Tentacles. — The tentacles are short and obtuse, with thin walls 



