46 THE VOYAGE OF H.M.S. CHALLENGER. 



posed of bundles of fibrillse, which are chiefly flattened in a lateral direction, so that 

 the stratum seems to consist merely of apposed bands of muscles. As each band is 

 repeatedly indented laterally, and can be dissected into separate pieces lying one below 

 the other, they give 'rise to the very complicated formation shown in fig. 10, which is 

 specially striking from the close apposition of the bundles of fibrillae. 



The bundles of fibrillse are more scattered in the younger animals ; smaller bundles 

 of fibrillge are also found here lying towards the ectoderm in the intermediate layer of 

 connective tissue. It is quite conceivable that these smaller bundles may have migrated 

 from the ectoderm into the mesoderm, in order to supplement the mesodermal muscular 

 layer. The state of preservation of the material did not allow me to confirm this sup- 

 position, as I could not make out whether or not radial muscular fibres were persistent 

 in the ectoderm. In the peripheral part of the oral disk the bundles of fibrillae pass 

 into the tentacles, where they preserve exactly the same arrangement and position in 

 the mesoderm. 



The corona of tentacles is immediately contiguous to the wall, whilst in Tealia 

 crassicornis, wliich in other respects is not unlike Dysactis in its general habit of body, 

 it is separated from the wall by a portion of the oral disk capable of becoming pleated. 

 The corona consists of several hundred tentacles, which are distributed in four to five rows, 

 and decrease distinctly in size from within outwards. If we examine an animal which 

 is developed uniformly in all sextants, we find twenty-four tentacles in the first or inner- 

 most row, and twenty-four tentacles also in the second row, which alternate with the 

 preceding twenty-four. In the third row the number rises at once to forty-eight, which 

 are placed in such a way that they alternate both with the twenty-four tentacles of the 

 first row, and the twenty-four of the second row. In the fourth row the number is 

 again doubled, so that it consists altogether of ninety-six tentacles, which still alternate 

 with all the preceding tentacles. The last row is always irregularly developed; the 

 number of tentacles ought to amount to 192, but only came to some 90. 



It will be seen at once from this mode of arrangement that all the tentacles of 

 Dysactis — and this applies to almost all Actiniae — lie in difi"erent radii, and must therefore 

 belong to difi"erent radial chambers ; they are merely parts of a single circle which have 

 become distributed in difterent rows, from being displaced in the course of growth. It 

 follows necessarily, from the whole mode of arrangement, that the separate rows of 

 tentacles stand in regular relation to the radial chambers, as the same principle of 

 arrangement, viz., that each cycle contains the same number of units as all the preceding 

 taken together, applies to both. From my own observation in making preparations, 

 I am convinced that the twenty-four tentacles of the first series belong to the twenty- 

 four intraseptal spaces of the septa of the fii'st to the third orders, the next twenty -four 

 tentacles to the twenty-four intraseptal spaces of the fourth order, and so on. 



Exceptions occur to the conditions which I have laid down as regular, but these can 



