380 THE VOYAGE OF H.M.S, CHALLENGER. 



by several wedge-shaped radiating plates arranged in the form of a rosette ; and these 

 three ambulacra form together, at all events in the female, a special ambulatory surface. 



"The two ambulacral vessels of the ' bivium ' are also approximated along the back, 

 and thus the two interambulacral spaces on the sides of the animal, between the external 

 trivial ambulacra and the ambulacra of the bivium, are considerably wider than the other 

 three ; consequently, in a transverse section, the ambulacral vessels do not correspond 

 with the angles of a regular pentagon, but with those of an irregular figure in which three 

 angles are approximated beneath and two above. In the female the tentacular feet of 

 the dorsal (bivial) ambulacra are very short ; they are provided with sucking-disks, but 

 the calcareous support of the suckers is very rudimentary, and the tubular processes are 

 not apparently fitted for locomotion. In the males there is not so great a difference in 

 character between the ambulacra of the trivium and those of the bivium ; but the 

 tentacles of the latter seem to be less fully developed in both sexes, and I have never 

 happened to see an individual of either sex progressing upon, or adhering by, the water- 

 feet of the dorsal canals. 



" In a very large proportion of the females which I examined, young were closely 

 packed in two continuous fringes adhering to the water-feet of the dorsal ambulacra 

 (fig. 138). The young were in all the later stages of growth, and of all sizes from 5 up 

 to 40 mm. in length ; but all the young attached to one female appeared to be nearly of 

 the same age and size. Some of the mothers with older families had a most grotesque 

 appearance — their bodies entirely hidden by the couple of rows, of a dozen or so each, of 

 yellow vesicles like ripe yellow plums ranged along their backs, each surmounted by its 

 expanded crown of oral tentacles ; in the figure the young are represented about half- 

 grown. All the young I examined were miniatures of their parents ; the only marked 

 difference being that in the young the ambulacra of the bivium were quite rudimentary — 

 they were externally represented only by bands of a somewhat darker orange than the 

 rest of the surface, and by lines of low papillae in the young of larger growth ; the radial 

 vessels could be well seen through the transparent body-wall ; the young attached them- 

 selves by the tentacular feet of the trivial ambulacra, which are early and fully 

 developed. 



" We were too late at the Falklands (January 23rd) to see the process of the attachment 

 of the young in their nursery, even if we could have arranged to keep specimens alive 

 under observation. There can be little doubt that, according to the analogy of the class, 

 the eggs are impregnated either in the ovarial tube or immediately after their extrusion, 

 that the first developmental stages are run through rapidly, and that the young are 

 passed back from the ovarial opening, which is at the side of the mouth, along the dorsal 

 ambulacra, and arranged in their places by the automatic action of the ambulacral 

 tentacles themselves. 



"The very remarkable mode of reproduction of certain members of all the recent 



