Chap.II. RELATIVE POSITION OF THE AREAS. 27 



rows of suckers extending along the lower side of the future rays ; the rods are 

 placed exactly opposite what will hereafter be the extremity of the rays. 



It is apparent, from the above description, that the abactinal area (the rods), and 

 the suckers (the folds across the water-tube), are not situated in one plane, or even 

 in parallel planes. The arc containing the rods, and the arc passing through the 

 folds, make an acute, nearly a right angle, as is better understood by referring to 

 older stages. It will also be seen, by a glance at the drawings (PI. V. Figs. 1, 2, 3, 

 5 ; PL III. Figs. 7-10, t), that the folds denoting the place where the suckers will 

 make their appearance, and the rods (/, r") marking the position of the future rays, 

 are neither of them closed curves, but are always open, forming a sort of twisted crescent 

 shaped arc. I shall show how these curves become closed, when describing the 

 young Starfish immediately after it has resorbed the larva, and is ready to crawl 

 about by means of its suckers ; and point out the changes these parts undergo to 

 form diverging rays, also the manner in which the warped surfaces developing the 

 actinal and abactinal regions are brought into parallel planes. 



Relative Position of the actinal and abactinal Areas. — The folds of the water-tube {w'\ 

 which forms the actinal area, are not contained in one plane, but are placed upon 

 a spiral; the same is the case with the five limestone rods situated on the surface of 

 the other water-tube {w\ which forms the abactinal region. When we look at the 

 Brachiolaria from the side, that is, when facing the groove which separates the ven- 

 tral from the dorsal side, as in PI. IV. Fig. 4, or in the corresponding profiles, from 

 the side of the right and left water-tubes of PL V. Figs. 1, 2, 3, 5, 10, 11, 12, we 

 see either the actinal or abactinal side of the Starfish. We look in one case at the 

 water-tube (w) upon which is developed .the abactinal system ; while in the other 

 profile, drawn from the opposite side, we see the water-tube (w') which develops the 

 actinal system; the two water-tubes are placed on different sides of the stomach, and 

 have no connection whatever at this extremity, but are separated by the whole 

 diameter of the stomach, over parts of which these tubes have spread like a cap. 

 It will at once be noticed that, in any of these figures, each side of the future 

 Starfish makes an independent open curve; these curves form what appears to us, 

 when seen from the profile view, part of a circular arc. On looking, however, at 

 the same sides from the ventral or dorsal view of the larvae, as in PL IV. Figs. 1, 2, 

 or the corresponding views of PL V. Figs. 4, 6, 7, 8, 9, 13, 14, we do not see the 

 arc formed by these sides projected as a simple straight line, as it would be were 

 it all contained in one plane. The extremities of the arc, both of the actinal and 

 abactinal area, — that is, the two ends of it which are nearest, one to the water-pore, 

 and the other to the anus, — are seen, as in PL V. Figs. 1, 2, 3, 5, 10, 11, 12, one on 

 one side of an axis passing through the centre of symmetry of the Brachiolaria, 

 and the other on the other side. The only curve which fulfils the conditions of 



