394 WILSON. [Vor. IX 
which in these sponges send a special little canal to each 
chamber (see Schulze’s figure of Euspongia. Zezt. f. Wess. 
Zool, Bd. XX XW; Vat. XXXVI Pies 2); ) The 2ditference 
between the two canal systems is easily explained, that of 
Euspongia being derived from the type shown in Fig. 5, by the 
pushing out of minute diverticula from both afferent and 
efferent canals. 
Having now obtained a generalised idea of a complex non- 
calcareous sponge, it will be found a simple matter to compare 
such a form with a Leucon colony, of which I give a surface 
figure, taken from Vosmaer, in Pl. XXV, Fig. 6. The structure 
of the silicious sponge is readily understood if we suppose it to 
be a colony, in which the limits of the individuals have been 
lost or obscured by the increasing thickness of the walls of 
adjacent individuals. This increasing thickness would finally 
result in a more or less complete fusion of the members of a 
colony into an undivided mass with oscula scattered over the 
surface. Each of the main efferent canals of the silicious 
sponge is homologous with the paragastric cavity of a single 
Leucon. Both the canal and its set of branches, though, are 
extremely irregular, having completely lost the symmetry of 
the ancestral type. The flagellated chambers, however, still 
bear the same relation to the efferent canals as they did in the 
Leucon, z.e. they are simple diverticula of the canal wall. The 
system of afferent canals is obviously homologous with the 
same system in the Leucons, bearing identically the same 
relation as in the latter group, both to the flagellated chambers 
and the efferent canals. The subdermal chambers, communi- 
cating with the exterior by numerous pores, though a late 
acquisition, are found in certain Leucons, e.g. Eilhardia 
Schulzei (Polejaeff, Pl. IX). 
In many of the non-calcarea the colonial nature of the sponge 
is indicated by the presence of elevations (oscular tubes or 
papillae) bearing oscula on their summits. But the number of 
oscula is not always to be taken as indicating the number of 
individuals of which the sphere is composed, for the colonies of 
calcareous sponges show plainly that the budding individuals 
do not always develop oscula. And on the other hand there 
