EMBRYOLOGY. 
Sjpong. 11 
The author considers pores and oscula as essentially similar structures, 
and disagrees with the view that in a Sponge with many oscula, each 
osculum is the sign of a Spongozoon. Description of spermatozoa of 
Reniera simulans , p. 103 ; of Amorphina panicea and coalita , p. 112. 
EMBRYOLOGY. 
Delage finds that in the larva of Esperella the ciliated cells do not con- 
stitute the superficial layer of the body, but they are covered by an 
external layer of cells, representing the ectoderm, which are much larger 
than the ciliated cells, and rounded. These ectoderm cells do not touch 
one another but form a discontinuous layer. The central mass of the 
larva is formed of scleroblasts, connective tissue cells, and large cells with 
a clear nucleus, the mother cells of the chambers. The ciliated cells repre- 
sent the endoderm. They travel to the interior and clothe the canals. 
The chambers are not endodermic, but formed in the manner of schizo- 
coelic lacunes, lined by mesoderm. The larva fixes itself by any point of 
the surface of tho body. 
The larva of a siliceous Sponge may be compared to that of a Sycon, in 
which the ectoderm, instead of being localized at one pole, is spread as a 
thin discontinuous layer over the ciliated cells. The endoderm cells, 
instead of being invaginated en masse , leave the surface singly. 
Dendy (3) describes the pseudogastrula stage in Grantia labyrinthica, 
= Teichonella labyrinthica , Carter. The embryo lies in a cavity in the 
maternal tissues, which is lined by a distinct layer of flattened endo- 
thelium, and is situated in the thin layer of mesoderm between the ciliated 
chamber and the spicules. The embryo is so placed that the ovoid 
granular cells are turned towards the spicules, and the columnar endoderm 
towards the flagellated chamber. As the embryo grows, it causes the 
collared epithelium of the chamber to bulge out into the flagellated 
chamber, and form a kind of blister. The opposite side of the embryo, 
turned towards the layer of spicules, becomes flattened. In the youngest 
embryos (fig. 1) the ovoid granular cells form a single layer, and the 
segmentation cavity contains finely granular, gelatinous-looking tissue, in 
which are visible nuclei, probably mesodermal, but of uncertain origin. 
As development goes on, the granular cells proliferate rapidly, and occupy 
more space, and hence, as they cannot project outwards, owing to the 
rigid layer of spicules beneath them, they become invaginated, and give 
rise to the pseudogastrula. The pseudogastrula is thus due to a 
mechanical invagination of the layer of granular cells caused by their 
active growth, and the peculiar situation of the embryo. These cells 
now form a layer several cells thick. The embryo is now set free by the 
rupture of the wall of the flagellated chamber. The segmentation cavity 
is at this stage reduced to a mere slit, but when set free the embryo 
becomes nearly spherical, and the granular cells form a hemispherical 
mass composed of (1) an external single layer of clearer cubical cells ; (2) 
an internal mass of granular cells, more or less polygonal from mutual 
