cane MIDLAND NATURALIST. 
will prove more satisfactory. If he has the conveniences o£ a biologi- 
callaboratory at his disposal, he will want to make sections, and 
this does not present difficulties that would prove unsurmountable. 
A bit of the alcohol specimen may be stained with borax carmine 
and imbedded in celloidin and good sections may be made with an 
old microtome blade. The siliceous or glassy spicules will certainly 
spoil somewhat his best knife, but then in every laboratory there 
are a few knives reserved for just such kind of work. I have even 
made fair free hand sections of the gemmules, that will show the 
arrangement of the birotulate spicules which form the rather thick 
wall of these objects. 
In examining a bit of sponge under the microscope, we will at 
once notice two structures viz., the skeleton part and the sarcode 
or fleshy part. The fleshy portion is supported by a siliceous 
framework made up of fine delicate, needle-like spicules—these 
spicules are about one-hundredth of an inch in length and pointed 
at both ends as a rule; in some species the spicules will be found to 
be covered by minute pointed projections and giving them a thorny 
appearance. -The shape, size and appearance of these spicules help 
to determine the species. Besides these skeletal spicules there are 
others somewhat different in appearance and they are found in the 
dermal layer and hence called ‘‘ dermal spicules." In the walls of 
the gemmules are found a third kind of spicules called ‘‘birotulates,’’ 
these are somewhat of the shape of dumb-bells, but the ends instead 
of being knobs are either circular disks, or toothed disks or even a 
circle of kooklets. These birotulates are very important in classi- 
fication. Carter selected them as the basis for the diagnosis of the 
genera of Spongillidae. : 
In order to determine the genus and species of any Fresh Water 
Sponge, there should be made four microscopic preparations : 
‘The first is to examine a small piece of the dried sponge 
mounted directly in balsam. 
, 
_ latter preparation is made by placing a mass containing eight or ten 
se on a slide and applying some hot nitric acid to it — 
r 
er the acid has acted for a time, it may be washed 
by applying alcohol and then absolute 
in balsam. 
mount in 
