No.3. ] DEVELOPMENT OF MARINE SPONGES. 36 I 
diverticula, may be formed from groups of mesoderm cells 
(Esperella, Tedania, Chalinula fertilis, Myxilla). 
3. The afferent canals, including the subdermal cavities, 
instead of being formed as invaginations from the ectoderm, 
arise as lacunae in the mes-entoderm (Esperella, Tedania, 
Esperia, Stelletta, Myxilla). In Reniera filigrana (Marshall) 
they are formed as entodermic diverticula. 
The coenogenetic development of the flagellated chambers 
and efferent canals suggests, as I have said, an essential 
similarity of nature in the so-called entoderm and mesoderm of 
sponges. This belief, so long upheld by Metschnikoff, derives 
some of its strongest support from this author’s physiological 
investigations (see azte, p. 359), as well as from the fact, first 
emphasized by Metschnikoff and Barrois, that in the most 
common sponge larva (the solid larva) mesoderm and entoderm 
form a single indivisible layer. 
And likewise the development of the afferent system of 
canals, in some sponges from the ectoderm, in others from the 
mes-entoderm, may possibly be taken as meaning that even 
these two primary layers (the outer and the inner) are not 
distinctly differentiated from each other in the sponges ; or, in 
other words, that the mes-entoderm is still enough like the 
ectoderm to form organs ordinarily produced by the latter 
layer. 
There is another (hypothetical) way of explaining these 
phenomena, which consists in supposing that ectoderm cells of 
the larva migrate into the interior, and, although indistinguish- 
able from the surrounding mes-entoderm cells, alone take part 
in forming the afferent canals. Similarly we may suppose that 
in the solid mass which constitutes the parenchyma of Esperella 
there are two radically distinct classes of cells, one of which is 
potentially gifted with the power of forming efferent canals 
and flagellated chambers, while the other has not this power 
and must remain as amoeboid mesoderm. But this is pure 
hypothesis. 
The result of this critical examination seems to be that the 
Olynthus must be regarded as the ancestor of sponges (Haeckel, 
Kalk-spongien), and that the entoderm and mesoderm are not 
