Genera Axinella, Phakellia, Acanthella a. o. 317 
solid. Moreover it is said that the extra-axial skeleton forms a 
network (more or less in Azxinella). I think Pıck was right in 
removing the species from Raspazlia. 
Resuming we formulate the following table (p. 12—13): 
Technical note. 
For the study of the skeleton of sponges it is not sufficient to 
prepare sections. The spicules have to be carefully isolated by 
boiling a piece of sponge in diluted hydrochloric or nitric acid; they 
are afterwards washed, dried and mounted in balsam, unless certain 
details in structure are to be studied. For such purposes I have 
given other methods. In order to determine the sort of spicules, 
which oceur in a certain sponge it is, however, quite sufficient to 
mount in balsam. Transverse and longitudinal sections inform us 
how the distribution and the arrangement of the various spicules 
are. Herefore it is absolutely necessary to make, in addition to the 
ordinary thin sections, thick and very thick sections (50—500 «u and 
sometimes more). In many cases this is even not sufficient. Pre- 
parations have to be made of the skeleton devoid of the “soft parts”. 
The sponges are dissociated in diluted ammonia or caustic potash. 
For some sponges the best results are obtained by taking fresh 
specimens, which are then treated as a whole with cold or warm (60°) 
potash (1—5°/,); other species are better first preserved in alcohol 
and afterwards treated with potash or ammonia. This process demands 
often much patience, for one has to watch them carefully. I usually 
try now and then how far maceration is going on by producing a 
current of fluid on the sponge with a pipette with narrow opening. 
If the maceration is proceeding one sees clouds of sponge-substance 
coming out. If the skeleton becomes visible one better removes the 
sponge from the solution and farther proceeds under water. I cannot 
give a fixed rule; it has to be found out for every species. Many 
Axinellae I kept for days or weeks in running water, before the 
skeleton was really “clean”. Other sponges are ready within a few 
hours or a couple of days. If one has time to wait, very beautiful 
skeletons can be had by placing the fresh sponge in a week solution 
of formol (to begin with 4, then 2°/, formaldehyd). Of course it is 
only possible to prepare skeletons in this way of we have to do 
with sponges the spicules of which are kept together by some sub- 
stance, say spongin. It must, however, be born in mind that in many 
case sponges contain spicules losely dispersed in the parenchyma, in 
