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ferent from its primary appearance, being too round* and filled 
with the granular germs, whereas the locomotive gemmule ig 
at first oval, having only its lower portion of an opaque white, 
which contains its reproductive or vital substance. These may 
be seen in M. Laurent’s beautiful plates. I must, indeed, 
remark that the Professor’s fig. 1 7 is good, and accurately shows 
how the young Spongilla ” is developed from a seed-like body, 
and much in accordance with my own description (at p. 373^ 
Lin. Trans, xviii.). 
Professor Williamson makes no mention of the currents of 
water, which at times are seen to enter into, and flow from, the 
living mass of the river-sponge ; but, inasmuch as so many 
parasitical insects, infusoria, aquatic mollusca, &c., inhabit the 
substance, it is exceedingly difficult to know how far they cause 
the influent and effluent streams by their process of branchial 
respiration, and how far (if at all) they are effected solely by 
the sponge-mass itself. It is almost always the case that some 
small insect may be detected, either nestling in the pores of the 
Spongilla or burrowing at the base of the mass ; and I have 
not unfrequently found in some specimens, many of the Ophry 
dince of Ehrenberg, embedded in the jelly, or parenchyma, of 
the mass. So, again, may some of the minuter Amoehcey 
Actinophrys, or infusorian animalcules, be confounded with 
what Carter terms cells,” or sarcoids, or small detached 
ciliated pieces of sarcode,” assuming those forms. Professor 
Williamson admits this great difflculty, which I had long ago* 
experienced in my earlier researches, unaided with a powerful 
microscope; and he well says : Various infusorial animalcules 
find their way into the sarcode of Spongilla, which may readily 
be mistaken for essential parts of the organism.” Lieberkiihn’s 
notices of numerous groups of germ-cells,” or “ germ- 
granules,” I am not as yet acquainted with. 
In concluding these supplemental remarks on Professor 
Williamson’s interesting account of the Fresh-water Sponge,’^ 
I may mention a recent handsome work on the Sponges of the 
Adriatic,” although it is unfortunately written in Grerman. It 
is entitled, ‘‘ Die Spongien des Adriatischen Meeres, von Dr.. 
Oscar Schmidt,” Leipzig, 1862-6, and is illustrated with many 
beautifully coloured plates. Also another ably illustrated mono- 
graph, Les Spongiaires de la Mer Caraibe,” by MM. Duchas- 
saing et Michelotti, published in Naturk. Verh. Holland 
Maat. Wet. te Harlem, vol. xxi. 1864. 
Professor H. J. Clark (of Pennsylvania) remarks in his paper 
‘‘On the Spongice ciliatce,'’ p. 133, “Annals and Mag. Nat. 
* This fig. 13 seems to be meant for the largest, and more mature of the 
germ-like bodies (see Lin, Trans, xviii. p. 374.) 
