298 W. WOODLAND. 
which, in virtue of their acuteness, are best able to cleave a 
passage. In connection with this last principle, it may be 
poiated out that the form of the Alcyonarian spicule certainly 
suggests the idea that the minor processes (doubtless due to 
that localised activity of the protoplasm which remains un- 
absorbed in the prolongation of the main branches) may be 
attributable to the same cause as say the lobose pseudopodia 
of a rhizopod—the protoplasmic investment of the spicule 
being comparable to the ectosare in which the protrusive 
movement originates, and the deposited calcareous matter to 
the stream of endosarcal granules which follows in its train,— 
and in all probability there does exist an affinity between the 
two kinds of emergencies. 
As has already been described, the extremities of the 
young dumb-bell spicule quickly become amphiccelous in 
character, or, in other words, a broad rim usually develops 
around the hemispherical ‘‘ head ” of each dumb-bell render- 
ing the terminal surface more or less concave (fig. 3), and a 
few minor processes developing at the “corners” of the 
spicule, the entire structure comes to resemble, as also before 
remarked, a caudal vertebra. A possible explanation of this 
change from the simple dumb-bell to the amphiccelous con- 
dition is to be found in the fact stated above, viz. that the 
consistency of the mesoglceal substance is largely solid, and 
not liquid in nature (figs. 16 and 17), from which it follows 
that in the elongation of the binucleated scleroblast and its 
contained sclerite, the resistant pressure offered by the 
mesoglea is greatest at the extreme ends of the 
spicule, and therefore less towards the sides (i.e. the 
pressure is not the same at all points as would be the case 
were the medium liquid), and seeing that, at the same time, 
the mass of the protoplasm is situated towards the 
extremities (being pushed somewhat to the sides however 
by the terminal pressure), further deposition of the calcareous 
substance must, under these two conditions, take place at the 
sides and towards the ends of the spicule, i.e. the 
terminal surfaces will become amphiccelous (see text-fig. B). 
