RESTITUTION-BODIES AND FREE TISSUE-CULTURE IN SYCON 315 
E.g. in Pennaria the endoderm cells enter in large numbers 
into the composition of the restitution-masses, and are distin- 
sushable immediately after dissociation by large granules. 
Within twenty minutes, however, a syncytial mass has been 
formed, in which very few of these granular elements can be 
distinguished. Presumably the granules have been resorbed in 
the new conditions. On the other hand, neither his observations, 
nor those of de Morgan and Drew, in the least exclude the idea 
of migration of ectoderm or endoderm cells to thei proper 
stations after intra-typical dedifferentiation. 
In this connexion, the facts concerning the possible attrac- 
tion of the various types of cells for each other may be men- 
tioned (Huxley, 8). In cultures consisting almost entirely of 
collar-cells, a small proportion of normal regenerates usually 
occurred. In other cultures made at Plymouth, where the 
great majority of the masses were choanocyte blow-outs, with 
partial dermal covering, a small proportion were dermal 
blow-outs. These facts may be due either to accidental distribu- 
tion of dermal cells, or else to an attraction of dermal cells for 
each other. This point could only be settled by appropriate 
experiments. The probable attraction of spermatozoa by 
choanocytes was mentioned in the same paper. 
(b) Formation of Blow-outs. 
The secretion of fluid by epithelia, whether dermal or choano- 
cyte, and consequent formation of spheres or segments of 
spheres (* blow-outs ’), is an interesting phenomenon. 
In this connexion, Mr. J. Gray, of King’s College, Cambridge, 
has kindly allowed me to refer to some unpublished observa- 
tions of his own, which he is at present investigating, on the 
formation of similar blown-out spheroidal masses by fragments 
of the gills of Mytilus. The phenomenon would thus seem to 
have more than isolated significance. It perhaps involves 
changes of the same nature as those taking place in the forma- 
tion of a blastocoele. 
