164 Dr. W. Marshall on the 
minishing centripetally, but that they appear zigzagged and 
always so that in two neighbouring lines the opposite angles 
of the zigzag have their apices either turned towards or away 
from each other; and at the same time it is observed that the 
angles of two horny lamellae which are turned towards one 
another are united by transverse floors; in other words the 
entire capsule of the gemmule consists of a system of little com- 
partments inserted into each other in accordance with the three 
dimensions of space, and gradually diminishing in the thick- 
ness of their walls and in their dimensions from without in- 
wards. ‘The superficial compartments are hollow, and in the 
dry state, which alone we have here to take into consideration, 
filled with air; the innermost are solid; their form is that of 
a hexagonal prism terminated at each end with six faces, the 
longitudinal diameter of which lies tangentially to the sphere of 
the contents of the gemmule. These compartments are certainly 
not modified cells, but, like the innermost independent horny 
layer of the whole capsule, a cuticular formation. Their sub- 
stance is structureless and very strongly refractive; it resists 
calcination remarkably, becomes brown without shrivelling, 
and during this process only the angle-lines stand forth 
strongly, especially of the angles of the compartments in which 
several walls meet together from different sides. Hydrofluorie 
acid has a peculiar effect upon this substance ; by treatment 
therewith it loses its strong refractive power and also some- 
what of its yellowish colour, and especially its brittleness, for 
which reason in gemmules treated with hydrofluoric acid we see 
the radial lines of contact of the compartment-columns brought 
much closer together, and the compartments, often enlarged 
in aradial direction, in general, but especially in the peripheral 
layers, much more irregular in form. Henceit seems to me 
not improbable that a strong percentage of silica is proper to 
this substance. Externally and internally the compartment- 
layer of the capsule is surrounded by a system of tangentially- 
placed but otherwise irregularly-arranged siliceous spicules, 
beset at both ends, even as far as the middle, with fine spi- 
nules curved inwards. ‘The spicules adhere more firmly to the 
inner surface of the compartment-layer than to the outer surface 
of the firmer horny layer in immediate contact with the 
germ, which exhibits a fine concentric striation, and on the 
outside fine irregularly-placed pits, the impressions of the 
spinules of the inner tangential spicules. ‘This is easily seen 
in sections through the gemmules, in which the inner layer 
readily separates from the compartment-layer. 
‘Lhe aperture of exit for the germ when awakened to life 
is round, and passes through both layers of the wall; but it 
