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



previously treated with chromic acid. The former were unfortunately of absolutely no 

 use, their tissues were macerated, and the form of the body disfigured by pressure almost 

 past recognition, whilst the latter permitted a detaUed description of the body form and 

 of many anatomical conditions ; the septa had, however, suffered severely in preservation, 

 which, as I have noticed, is usually the case in material prepared by means of chromic acid. 



Making allowance for changes caused by pressure, the form (PI. II. fig. 7) is the same 

 in all the specimens. The body begins with a relatively small, firmly attached base, rises 

 to a considerable height, and gradually expands like a stemless chalice up to the oral disk, 

 which unfolds like a flower. This form is rare among the Actiniae, especially in con- 

 tracted animals, since, on the other hand, the inversion of the margins of the oral disk 

 usually causes the body to diminish in size upwards like a cone. 



The ectodermal side of the pedal disk (PL IX. fig. 5) is covered with numerous (more 

 than a hundred) radial ridges, which begin at the margin, and, partly at least, extend as 

 far as the centre. They form a very dainty figure, as they have a vandyked, wavy course, 

 and project with unusual sharpness above the level of the disk. On the endodermal side 

 there are strong muscular cords, piercing the bases of the septa in bundles (fig. 4) ; they 

 are crossed by other muscular cords, which pass transversely through the pedal disk from 

 the endodermal to the ectodermal side. These perforating muscular fibres originate from 

 the two muscular layers of the septa ; this is best shown in transverse sections taken per- 

 pendicularly to the direction of the septa (fig. l). Some of the longitudinal and of the 

 transverse fibrdlae diverge and reach the mesoderm in bundles ; their fibrillae become inter- 

 mixed, as they become interwoven with one another and with the layer of the basal circular 

 muscles. The bundles then run towards the depressions which separate the ridges on the 

 ectodermal side, and become fastened at the bottom of them ; here they split up into the 

 fibrillae of which they are composed (fig. 7), so that their ends appear to be dendritically 

 branched, and remind us of the ends of the muscular fibres of the Ctenophora. 



As the perforating bundles originate from the muscles of the septa, it naturally follows 

 that they are arranged regularly in radial rows. Each septum has two hardly separate 

 corresponding rows, one of which is derived principally from the transverse muscles, 

 the other principally from the longitudinal muscles. This is seen in the section which I 

 have given in fig. 3, and which was taken parallel to the boundary surfaces of the pedal 

 disk. As the section has fallen somewhat obliquely, we see at one end the bases of the septa 

 cut through obliquely, then the circular muscles intersected by the bundles of perforating 

 muscles, and, finally, the bundles running in two rows through the supporting substance. 



Both the intersecting bundles of muscles and the depressions on the surface of the 

 pedal disk (fig. 1) are wanting below the beginnings of young septa. This shows that 

 the muscular layers of the septa only grow secondarily into the supporting substance, 

 and that the depressions on the surface are occasioned by their becoming fastened to 

 its ectodermal side. 



