of the Fibre in the Spongida. 117 
pigment having passed into the kerasine. The faint lineation 
of the colourless cellular structure in the fibre of Aplysina 
fusca (fig. 11, 6, ¢c), although too distinct for representation, 
nevertheless presents somewhat of the appearance in form of 
that of Janthella in the transverse section (fig. 14,6). I 
should also mention that in the abortive (?) horn-cells of 
Aplysina purpurea many of the granules of the axial substance 
often present a dark purple colour like those of the pigmental 
cell, and that, in size, the smallest horn-cell hardly exceeds 
the dark pigmental cell itself (fig. 1, 7), im which, too, 
the dark purple granules are most distinct ; so that it seems as 
though the horn-cell originated in the pigmental one ; and yet 
there are no dark-purple pigmental cells to be seen in the 
horny fibre of A. purpurea as in Lanthella, although the sar- 
code of the former is equally charged with them (see a descrip- 
tion of the pigmental cell, anté, p. 104). 
As the spicules formed by the sponge itself have been men- 
tioned among the “hard parts” of which the skeletal struc- 
ture is composed, it may not be without interest to add here 
that they appear to be developed in a similar way, although 
certainly, in some instances at least, first originated in nucleated 
cells and then ejected into the sarcode or parenchyma for 
completion (‘ Annals,’ 1874, vol. xiv. p. 100, pl. x. figs. 3~ 
15, and pl. xxi. figs. 26, 27); also that, occasionally, ar- 
rested spherical, elliptical, and elongated forms of the spicule 
are present analogous to the “ horn-cells’’ above mentioned 
(fig. 15). This is particularly the case in a specimen of 
Dictyocylindrus laciniatus from the Mauritius, to which I 
have before alluded (‘ Annals,’ 1879, vol. iii. p. 297), as it 
is with the “horn-cells” in the specimen of Aplysina pur- 
purea from Trincomalee. Further, it may be observed that 
the ornamental parts of the spicule are the last parts added to 
its structure (ez. gr. the small spines on the anchoring-spicule 
of Hyalonema, * Annals,’ 1873, vol. xii. p. 371, pl. xiv. 
fig. 9, f, &c.), and that the horny fibreis frequently accompanied 
by a foreign body attached to its surface by an extension over 
it of the last formed horny lamina, indicating in either instance 
that the sarcode or parenchyma, at least, has the power of 
producing both substances (‘ Annals,’ 1872, vol. x. pl. vii. 
fig. 4, /). E 
Analogous, however, as the sequential growth of the fibre 
and the spicule in the sponges may be, they are not homolo- 
gous, any more than the bones and ligaments in the higher 
animals; and but for a single instance, viz. that pub- 
lished in 1865 by Fritz Miiller in Darwinella aurea (Archiv 
f. mikroskop. Anatomie, Bd. i, p. 344, Taf. xxi.), wherein 
