6 
POPULAR SCIENCE REVIEW. 
the latter instead of internal. On this point further observations 
are much needed ; but both Carter and Lieberkuhn have noticed 
this tendency to form compound groups of sarcoids. It is evi- 
dent that a period arrives when the Spongilla exhibits a disposi- 
tion to break up and allow the ciliated cells to move off as 
independent individuals. When they do so each one becomes 
more or less pedunculated (fig. 19), contains a contractile vesicle 
or vesicles, as well as a remarkable greenish granule, is polymor- 
phic, and by means of its single cilium sets up distinct currents 
(fig. I9d) in the surrounding water. But besides these single 
protoplasms there are occasionally compound groups which 
become detached under another shape. Ehrenberg described, 
under the name of Uvella, a genus of infusorial creatures, which 
formed clusters of monads radiatinof from a common centre to 
which they were all attached. Similar clusters sometimes pre- 
sent themselves on the breaking up of Spongilla (fig. 20). These 
were noticed by Carter, and similar groups were observed by 
Lieberkuhn amongst what he regarded as spermatozoa. How 
far the Uvella-like arrangement of the ciliated groups seen by 
these two observers represent the same thing is uncertain, but 
both indicate a disposition in Spongilla towards these radiant 
arrangements. Under other circumstances detached portions 
assume the form of Actynophrys (fig. 21), as is not uncommon 
amongst other rhizapods. The observations of Lieberkuhn have 
revealed some interesting facts additional to those recorded by 
Carter. He shows that in many cases the living Spongilla is 
supported upon a dark brown earthy mass, often several inches 
thick, consisting of empty shells of gemmules with their amphi- 
discs, various siliceous needles, and decayed sarcode. In these 
dead portions the gemmules are particularly abundant. In the 
deeper parts of the living sponge and in the neighbourhood of 
the dead portion he found, in addition to the ordinary brown 
gemmules, others of a shining white colour, and some in which 
the outer shell was exceedingly thin and easily broken up. On 
dissecting portions of the sponge containing these peculiar 
objects under water, he obtained isolated whitish ill -defined 
globular pieces, of about the size of the gemmules, and which he 
believed to be the latter bodies in an imperfect state of develop- 
ment. They distinctly exhibited two substances entering into 
their composition — viz., an outer one having about the same 
refractive power as the ordinary cells of the sarcode, and an 
inner mass which was highly refractive. Both these layers re- 
solved themselves, under pressure, into aggregations of cells. 
The inner ones corresponded very closely with those already 
described from the centre of the brown gemmules, adhering 
firmly together, refracting the light strongly, and having large 
fat-like granules interspersed. These cells or sarcoids were like 
