Dr. W. Marshall on new Siliceous Sponges. 393 
are several series of forms which may be derived from differ- 
ent although perhaps nearly allied marine ancestors, the peculiar 
resemblances of which would then be rather apparent and 
acquired by similar adaptations, and consequently resting on 
analogy, but not inherited in common, and consequently homo- 
logous ; in other words, that the freshwater sponges had not a 
monophyletic, but a polyphyletic origin. It seems to me worth 
while to dweil for a moment upon this consideration, and to 
weigh the pro and contra of these two possibilities. Although 
at the outset I see clearly enough that at present no definitive 
settlement of the question with demonstrative force can be 
arrived at, and that perhaps such a settlement never will be 
attained, this shall not prevent me from placing side by side 
with the current hypothesis (for the assumption of a mono- 
phyletic family of ‘ Potamospongie ” is no more than this), 
another one which perhaps may be no better, but is certainly 
not worse. 
If we ask, in the first place, in what do the different sili- 
ceous sponges of the freshwater agree? the answer is, in 
three points :—first, they are Monactinellids; secondly, they 
inhabit the fresh water; and thirdly, most of them, besides 
sexual reproduction, present an asexual reproduction by means 
of special buds (gemmule, spherule, statoblasts, &c.) provided 
with a more or less developed siliceous armature, which are 
developed at certain seasons at the expense of the parent ani- 
mal, and are usually associated with the decay of the latter. 
The first two points are wholly irrelevant in judging of the 
relationships of the so-called Spongille ; as a matter of course 
these are certainly more nearly allied to a Véoa or similarly 
aberrant Monactinellid (always supposing that these are them- 
selves really of monophyletic origin, which, from my observa- 
tions, I have good cause to doubt) than to a Tetractinellid or 
Hexactinellid; but for the recognition of the phylogenetic 
relations of the individual species to each other and to the 
legions of marine Monactinellidee (which, so far as we can 
see at present, form at least 75 per cent. of the living siliceous 
sponges), we do not gain much from them. The second 
point, the residence in fresh water, will hardly be seriously 
regarded by any one as coming into the balance ; from this we 
can only conclude that there are sponges, as well as numerous 
other inhabitants of salt water, which are able to adapt them- 
selves in this particular *. There remains therefore only the 
* See the valuable memoir by E. von Martens in the ‘ Archiv fiir 
Naturgeschichte, 1857, p. 149, in which, however, no consideration is 
iven to the sponges, which indeed at that time were not universally 
admitted to beanimals. See also Semper, ‘ Existenzbedingungen,’ pp. 180 
281, 11. 125. 
Ann. & Mag. N. Hist. Ser. 5. Vol. xi. 29 
