remarkable Species of Cliona. 63 
In fig. 24 a short conical spine ‘projects from the fusiform 
part of the shaft—a bud-like process, which, if prolonged, would 
give our uniaxial spicule a decidedly biaxial appearance, 
This budding of the spicules is one of the commonest of phe- 
nomena amongst the Spongide. In Geodia arabica 1 have 
seen a variety “of one of the large anchoring spicules which, 
had developed a fourth fluke, and so become four- instead of 
three-pronged ; and, similarly, i in a Stelletta | once observed a 
variety of the trifid bifurcate anchoring spicule in which an 
additional bifurcate arm had put in an appearance, so that 
the spicule had become quadrifid: thus, then, our uniaxial 
spicules may become biaxial, and, likewise, quadriradiate may 
become quinqueradiate spicules. ‘The excessive variation to 
which sponge-spicules are subject makes it easy to conceive 
how the existing types of multiradiate spicules might have all 
originated from a primitive uniaxial cell. Let such uniaxial 
spicule-cells bud to a variable extent, some producing one, and 
others two, three, four buds and so on, and we should possess 
just the sort of material which, when submitted to the influ- 
ence of natural selection, would furnish us with the spicules 
of all our existing types,—to me apparently a much more 
natural way of jooking at things than that followed by Dr. 
W. Marshall. ‘This speculative observer considers that, 
in the case of the Hexactinellide, a sarcodic meshwork 
was first produced, which afterwards became silicified, and 
then broke down into separate sexradiate spicules. We have, 
however, every reason to believe that sexradiate spicules ori- 
ginate, like all others, in spicule-cells ; and Carter has actually 
seen the separate sexradiates of Aphrocallistes in various 
stages of cementation up.to their complete enclosure in a 
continuous siliceous network. Marshall’s view *, therefore, 
seems to me to reverse the case with a vengeance. 
In fig. 23 we appear to have two spicules joined together 
by their heads, though whether by ankylosis or as a result of 
budding, one cannot, in the absence of a visible axial canal, 
definitely say. In fig. 16 we have two shafts diverging at an 
angle of 60° from the same head; and as but one head is seen 
here, the case is probably one of mere budding. 
In fig. 24 the shaft of an ensiform spicule has lost its point 
and acquired a rounded termination like that of the mucronate 
spicules of C. mucronata, only without the mucrone ; at the 
* In reference to Marshall’s conception of the structure of Sclerotham- 
nus, I may here point cut that, when spicules grow together by ankylosis, 
their axial canals do not become continuous by opening into one another; 
on the contrary, while two or more spicules may become one, their canals 
always remain separate and distinct. 
