Gemmules of Freshwater Sponges. 167 
table. ‘Towards this little heap a very moderate horizontal 
current of air (the force of which, however, I had no means 
of measuring) was then directed by means of a pair of small 
hand-bellows, and this immediately caused its dispersal. This 
proceeding was repeated six times, and each time after the 
dispersion of the gemmules a pair of compasses was set in the 
middle of the spot where the little heap had been ; its legs 
were gradually opened at intervals of 1 centimetre, and curves 
were drawn upon the table. In this way were obtained ten 
curved regions each of 1 centimetre broad, and in these the 
gemmules were counted; then the mean of the six observed 
cases was taken and multiplied by two, in oxder to bring it to 
a percentage for each kind of gemmule. The following was 
the result :— 
| 10 
Regions of = 
1 centim. broad. 10h ea e l ie a a Mi = woe Total. 
Gemmules of | ee 
Sp. lacustris. { kg il iY Gl ei Mgt lel dal a 100 
Gemmules of 4 is 
Sp. nitens. 2 |} .. | 9 | 15 | 22 | 27 | 13 | 9 4 100 
These experiments, I readily admit, are very rough, but 
they do not seem to me to be absolutely valueless: this much, 
at any rate, may be learned from them, that the moving power 
of the wind acts more powerfully upon the gemmules of 
Spongilla nitens than upon those of S. lacustris; and to ascer- 
tain this was the purpose of the experiments. 
The gemmules of the other freshwater sponges* usually 
differ considerably from those of Spongilla nitens and Cartert. 
In no freshwater sponge known to me is the connexion of the 
gemmules with the rest of the body so intimate as in Par- 
mula Brownit, Bow., of which I have been able to examine 
three specimens from the Rio Negro, most kindly presented 
to the Leipzig Museum by Dr. Carl Miiller-Halle. Each 
gemmule, with its shell, is surrounded by a special capsule, 
which is never provided with an aperture, and which contains 
a very small quantity of horny substance, but is formed chiefly 
of naviculiform spicules, lying close together, like cobble- 
* IT have been unable to compare those of the genus 7wbella, Carter, 
and of the remarkable new North-American forms, 
