4-2 THE VOYAGE OF H.M.S. CHALLENGER. 



In the strongly contracted condition, shown by the specimen, the body appears to be 

 as hio-h as broad, and also of equal breadth in the region of the pedal and of the oral 

 ili-ks. On dissecting the animal, however, it becomes evident that if the height of the 

 animal is to be determined by the distance of the oral margin, from the pedal disk, it will 

 fall far short of the breadth, and, moreover, that the diameter of the contracted oral disk 

 is considerably greater than that of the pedal disk, which it must have exceeded twice 

 at least. When fully extended, our Actinia must have been shaped like a dish, the 

 wall diverging from the narrow base towards the broad oral disk. 



The wall rises from the margin of the moderately firm pedal disk, which measures 

 about 2 5 cm. in diameter, and is irregularly wrinkled and furrowed, to a height of about 

 3 - cm. ; it is covered with fifty -four longitudinal furrows, which are separated from one 

 another by equal intervals, and reach from the lower to the upper margin of the wall. 

 These longitudinal furrows are crossed in the lower part of the wall, by irregidar trans- 

 verse furrows, which become more indistinct towards the upper part. The wrinkled and 

 knobby appearance of the lower part of the wall thus produced I consider to be the 

 consequence of the high grade of contraction of the animal. 



The wall is firm like leather, but of no great thickness ; only that portion of it con- 

 tiguous to the oral disk is distended about 0"5 cm. by the contained mesodermal circular 

 muscle. The bundles of the latter are small, and composed merely of a few fibrillae ; they 

 run irregularly, either singly or united in groups in the fibrous connective substance. 

 They are separated from the ectoderm by a broad interspace, but extend nearly to the 

 circular muscular layer of the endoderm, and are even connected with it in some parts, 

 so that steady growth of the circular muscle undeniably takes place by the transformation 

 of endodermal elements into mesodermal. The principal mass of the circular muscle still 

 extends downwards a little way, in a layer of mesodermal bundles of fibres, lying close 

 under the endoderm. 



The oral disk bears fifty marginal tentacles, and is covered with an equal number 

 of radial furrows, which begin at the oral margin and end between each two 

 tentacles. The radial swellings lying between the furrows are flattest near the mouth, 

 and become more distinct in proj)ortion as we approach the tentacles. This proceeds 

 from the distribution of the muscles, which are very weak near the oral margin, and 

 become stronger towards the periphery till they swell out into the powerful muscular 

 masses of the tentacles. The muscular nbrillaB are remarkably strong, partly perhaps in 

 consequence of having swollen from the unsatisfactory state of preservation. Their 

 principal mass lies united in thick bundles in the mesoderm ; where the muscular system 

 is weak the bundles are scanty, and the separating tracts of connective tissue broad, whilst 

 towards the corona of tentacles the bundles lie close to one another, and the fundamental 

 substance becomes a slender framework. As muscular fibres still remain in the ecto- 

 derm the oral disk, if well preserved, would furnish an admirable subject for studying 



