RESTITUTION-BODIES AND FREE TISSUE-CULTURE IN SYCON 297 
appear to possess separate membranes. My attention, however, 
had not yet been drawn to this point, and I cannot be sure of 
it. Broken spicules were present in some. Another mass 
examined on the same day contained many more fragments 
of spicules. It was very similar to the first, but the epithelia 
were not so sharply marked off from the central masses, 
which in their turn were not quite so dense. When gelatinous 
membranes were present, numerous bacteria were usually seen 
along their outer edges. 
The spherules were of various sizes, as is shown in fig. 4, 
which illustrates an isolated specimen on the tenth day. his 
same specimen was examined again on the thirteenth day. 
The same individual spherules were identified, but their appear- 
ance had changed, their outlines being less regular and the 
general effect more transparent. On examination with a high 
power this was seen to be due to the fact that in the majority 
most of the individual cells had separated from each other 
(fig. 5). Hach spherule was surrounded by a definite layer of 
jelly. Within this, isolated clear cells, all sub-spherical, were 
scattered. At one point, either central or at the side, a denser 
yellowish mass was seen. This appeared to consist of larger 
cells, still adherent, containing many granules (of two types, 
large and small). A few of the small clear cells could still 
be seen embedded in some of the yellow masses. A minority 
of the spherules showed a different appearance (fig. 6). In 
them the spherule had simply subdivided into a small number 
of pieces, of somewhat irregular shape, each apparently con- 
sisting of clear cells round the periphery, yellow cells within. 
Vinally, one or two spherules intermediate in type were seen, 
i.e. with a few large masses and also some isolated clear cells. 
The independent gelatinous coverings of the separate 
spherules were also seen in other specimens, e.g. in that 
shown in fig. 2. 
A variant of the types already discussed is shown in fig. 8, 
which illustrates a small mass found in the culture-dish, 
consisting of an epithelium of dermal cells surrounding a central 
mass, presumably mainly of collar-cells, which had subdivided 
