218 
LIEBERKUHN, ON SPONGlLLiE. 
ciliated coverings of all Infusoria as yet known, and that of 
the Turbellaria, is a kind of epithelial layer upon which they 
are seated. This epithelium is composed of a single layer of 
spherical cells, about mm. in diameter, and which, though 
touching each other, are not in such close contact as to lose 
their rounded figure. Sometimes portions of this ciliated 
epithelium may be seen detached, and such detached frag- 
ments are often apparent in portions of the sponge which 
have been torn to pieces. They must not be confounded 
with the spermatozoids which sometimes adhere to detached 
amseba-like fragments of the sponge under the same circum- 
stances. Beneath the ciliated epithelium is a layer of sarcode, 
within which is contained what the author terms the medul- 
lary substance, which is of a spheroidal form, and occupies 
the whole interior of the spore. Its appearance differs 
greatly in different spores. The whole spheroid, which is 
whiter and more opaque at the hinder part, lodges extremely 
delicate siliceous needles, many of which, even at this time, 
exhibit the perfect form of the mature spicule. These siliceous 
needles are not disposed with any regularity in the spore. 
The main differences in the contents of the motile spores" 
arise from the greater or less abundance in them of " germ- 
granules." The fully formed " germ-granules " are usually 
spherical, more rarely lenticular. They attain a size of about 
-if^ mm., but some much smaller are met with. They exhibit 
a strongly refractive envelope and contents, which appear, 
when distinct, to resemble an iU-defined gelatinous globule. 
The number of these " granules " varies extremely in diffe- 
rent spores. They are sometimes also assembled into little 
rounded masses, composed of three or more together. These 
conglomerated germ-granules may sometimes be seen, to- 
gether with the siliceous spicules, escaped from the spore, 
and inclosed in a mucous, structureless case. Conglomerated 
granules of this kind are found in vast numbers in various 
parts of the Spongilla, but especially towards its base. But in 
all these instances the author has invariably also observed the 
ciliated spores. They appear, according to Lieberkiihn, to cor- 
respond with the isolated groups of germs, which, according 
to Carter, pass into the protean cells ; but an essential discre- 
pancy arises with respect to this, from the circumstance that 
this observer states that the groups of germs are produced im- 
mediately from the gemmules. This is at present unexplained. 
The zoosperms. 
Besides the ciliated bodies above described as being the 
agents of motion of the motile spores," Lieberkiihn ob- 
