Dr. W. Marshall on new Siliceous Sponges. 493 
freshwater sponges probably quitted the sea gradually and 
vcluntarily, and have adapted themselves in the course of a 
very long time; for, to say nothing of the Diluvium, sponge- 
spicules have been detected even in freshwater deposits of the 
Upper Jura*, the formation of which is long anterior to the 
origin of Lake Baikal. 
All these facts certainly prove the remarkable pliability and 
adaptability which are possessed beyond all other sponges by 
the Reniere, and these properties will very probably be the 
same all over the world. Under such circumstances, especially 
it we also bring in the structure of the freshwater sponges for 
comparison with the Lenderw, there is nothing more natural 
than to imagine that the former have originated from the 
latter, but independently of each other in different parts of the 
earth, and with the appearance of similar modifications tn 
structure and vital phenomena induced everywhere by adap- 
tation T. 
A part of these modifications are new acquisitions (e. g. 
gemimules), and therefore to a certain extent of positive 
nature; others, however, are of negative nature, and relate to 
the disappearance of peculiarities of the marine ender@, espe- 
cially to the loss of colour. Most ofthe 2endere occurring freely 
and at the surface are intensely and often even very intensely 
coloured (orange, red, velvet-black, &c.) ; and I have no hesi- 
tation about regarding these colours (as I have already done) 
as alarming or warning agents which deter other animals, 
not from eating the Reniere, tor they are not generally fit 
for food, but from injuring them in their existence by fruitless 
attempts to eat them. Now we know that retrogressions, 
* Young, Geol. Mag. 1878, p. 220. 
+ How great, indeed, the power of adaptation is in the freshwater 
sponges is strikingly proved by the interesting discovery of Dr. Joseph 
(59 8., B. d. schles. Ges. f. vaterl. Cultur im Jahre 1881, p. 253), who 
found in the Grotto of Gurk in Carniolia, an absolutely transparent (!) form 
of Spongilla (Sp. stygia, n. sp.). As I supposed that this freshwater 
sponge, which will find itself all the year round under the same, or nearly 
the same, conditions of existence, would form no gemmules, as these 
would be superfluous, I applied by letter to Dr. Joseph, who forwarded 
some preparations to me, and at the same time kindly wrote, among 
other things, as follows :—“ Your supposition that no formation of gem- 
mules takes place is correct, for neither in September nor in April did I 
Jind any.” Some people may perhaps think that the Spongdle of the 
Grotto of Gurk were not descended from ordinary Spongille, but directly 
from Monactinellidze of salt water, perhaps at a time when the waves 
of the Tertiary sea eroded the grottos of Carniolia and Friuli. This 
would have much less probability than the supposition that in conse- 
quence of uniform conditions of existence, not dependent upon the seasons, 
retrogression as regards the gemmules has occurred in Spcngilla stygia. 
} Zeitschy. f. wiss. Zool, Bd. xxxvii. p. 245. 
