Knowledge of the Spongida. 317 
venient structure for the situation of the pores. The spicules 
here are of two forms, viz.:—1, vermiculate, smooth, and 
cylindrical, sharp-pointed at both ends (Pl. XIV. fig. 9, a) ; 
and 2, acuate, smooth, curved or bent chiefly towards the 
blunt end (fig. 9, 6); the former 73 to 130 by 1 to 13-1800ths 
inch in its greatest dimensions, and the latter or acuate about 30 
by 1-1800ths; thus the former are imperfectly represented in 
Dr. Bowerbank’s illustrations (op. et loc. cit.), since the vermi- 
culate spicules here, viz. “5” and “6,” should have been 
sharp-pointed at each end, which would have been the case 
probably had they been boiled out of the microscopic fragment 
with nitric acid instead of mounted in the dried sarcode, where 
the draughtsman could not see that in the perfect form their 
ends were sharp-pointed *. The vermiculate spicules, which 
are by far the largest, form the base or axis of the “ scopiform 
portions,” and the acuates the echinating spicules, while both 
forms are indiscriminately mixed in the ‘ median” plane. 
Such are the characters of the structure in Phakellia venti- 
labrum ; but of course they may be more or less modified in 
other species of this family, since there may be only one form 
of spicule, viz. acuate, bent chiefly towards the thick end like 
the hilt of a pistol, which seems to be the most common situa- 
tion of the curvature in the Echinonemata; or this ‘ one 
form ”’ may be acerate, or the skeletal spicule may be accom- 
panied by flesh-spicules, as in the new species about to be 
described, viz. Phakellia ramosa ; still the way in which the 
echinating character is produced is always the same as that 
mentioned in the diagnosis of the family. Sometimes there 
is a transitional form of the spicule in which the acerate 
appears to be thickened and shortened on one side, so as to 
produce a kind of subacuate form (PI. XIV. fig. 14), which 
seems to explain how it is on the one hand that the spicule 
* The quickest way to examine a sponge is to soak a microscopic frag- 
ment of it in distilled water for from twelve to twenty-four hours; then tear 
it to pieces on a slide, drain, dry, and mount with balsam as usual; but 
to be certain of the exact form of its spicules requires that they should be 
boiled out with nitric acid, which may also be easily and quickly effected 
by placing the microscopic fragment on the centre of a glass slide and 
covering it with a drop or two of nitric acid, then boiling this over a 
spirit-lamp with low flame till it is nearly dry, after which the same pro- 
cess must be repeated twice or thrice ; and, finally, before the last drop of 
nitric acid is entirely dried up, removing the slide to the table, when, 
through gradually increased inclination and sufficient but careful edulco- 
ration with distilled water, the residuum may be freed from all remaining 
acid, drained, dried, and mounted in balsam; or, if desired, another 
microscopic fragment, prepared as first mentioned, may be added to it 
previously, when the perfect form of the spicules respectively, together 
with their position im s’tw, may be seen at once in the same preparation. 
Ann. & Mag. N. Mist. Ser. 5. Vol. xii. 23 
