128 THE VOYAGE OF H.M.S. CHALLENGER. 
directed upward and slightly inward, are placed round this semicircular margin and form 
an elegant fringe or comb, which closes over, as it were, upon the series of lamellee. 
On examining this organ microscopically, it is found that each line or lamella is made 
up of a series of small lamella, which are placed end to end together, and thus form an 
apparently continuous line. Each component part or small integral lamella stands 
upright upon its own rounded scale-like base; and the lamellar plates are made up of 
a single series of delicate rods united by irregular dissepiments, the whole structure being 
covered with a membrane, which appears to have been furnished with vibratile cilia. The 
scale-like plate which forms the basal portion is directly superposed upon the surface of 
the marginal plate, the parts occupied by the cribriform organ being slightly hollowed 
out for its reception. The outermost lines (pseudo-lamelle) are composed of thicker 
individual lamelle than any of the others, and these integral lamellze stand wider apart 
and resemble flattened spinelets, cach built up of several series of rods. On the upper 
portion of each line transition can be traced from the delicate lamella, above described, 
to the simple rounded cylindrical spinelets of the abactinal membrane. 
Judging from the position and character of this organ, as well as from its relation 
to the abactinal area, it is not improbable that it acts as a percolator; and in such 
a ease it might perhaps be looked upon as the homologue of the armature of minute 
ciliary spines which borders the vertical furrows that run between the consecutive mar- 
ginal plates in Astropecten and other forms. ‘These fringes of delicate miliary spinelets 
in Astropecten were regarded by Alex. Agassiz’ as probably the representatives in 
Asteroids of the specially localised bands of delicate ciliary spinelets known as “ fascioles,” 
which are present in many of the genera of irregular Echinoids. 
In species which have more than one cribriform organ in each interbrachial are (Plates 
XXL, XXII, XXIIL, XXIV., XXV., XXVI. and XXIX.), the additional ones occur on the 
vertical sutures immediately succeeding on each side of the median line, and are identical 
with the median organ just described. No case of irregularity or intermission occurs in 
any of the specimens I have examined. The number of cribriform organs present in each 
are appears to be always constant in a species; and species exist which possess one, 
three, five, seven, nine, or even fourteen of the organs respectively. The organ varies 
in the different species as regards its breadth, the number of vertical parallel lines or 
pseudo-lamellze which compose it, and the character of the integral calcareous bodies, of 
which these latter are formed (Plates XXVII. and XXVIII.) In Porcellanaster the com- 
ponent parts are more or less lamellar in form, as described above, whilst in the allied 
genera Hyphalaster, Styracaster, Thoracaster, the corresponding elements are papilliform 
(Plates XXVIII. and XXIX.) 
The Segmental Pits and Papille.—These are peculiar structures situated on the 
adambulacral plates and the mouth-plates (Plate XXVII. figs. 2, 3, 6, 7). They consist 
1 North American Starfishes, Mem. Mus. Comp, Zool., Harvard, 1877, vol. v. No. 1, p. 119. 
