C{ELENTERATA. PORIFERA

employed (besides the observation of the living larva in
hanging-drop moist chambers, oxygenated by means of a few
fronds of green alge), osmic acid followed by picro-carmine.
634. Gymnoblastic Hydroids (Tubularia mesembryanthe-
mum) (Ciamician's methods ').-For general observation of the
tissues, osmic acid of - to , per cent. For dissociation of
the tissue-elements, macerate in 1 per cent chromic acid, and
tease in dilute glycerin. It is advantageous to stain with
eosin in a very dilute solution before teasing.
635. Porifera (Ova of Chalina) (Keller's method 2).-Seg-
mentating ova are dehydrated in absolute alcohol, and then
cleared for examination in toto by placing them for two or
three days in a not too thick solution of sandarak, in which
they are then examined.
636. Porifera (Larve of Plakina) (F. E. Schultze's method 3).
-Blastule were hardened in osmic acid or absolute alcohol,
stained in toto with hiematoxylin, picro-carmine, or alum-
carmine; dehydrated completely, imbedded in paraffin, and
cut into sections with a Leiser microtome.
The best sections of the more advanced sessile larvie were
obtained by selecting larve that had settled down on thin
fronds of algo and treating them, together with the fronds,
with osmic acid, then alcohol of 52 per cent., alum-carmine,
Aq. dest., alcohol of 52 per cent., then 70 per cent., 95 per
cent., then absolute alcohol, turpentine, and finally paraffin.
1 Ibid., xxxii, p. 323.
2 Ibid., xxxiii (1879), p. 333.
3 Ibid., xxxiv (1880), p. 416.

391