XVII. SPONGIAC. 
8 Spong. 
kinds besides, viz. : Cyst cells, containing one large vacuole or several 
smaller ones ; sceletoblasts, producing some spongin, others spicules ; 
ova (various stages of development) ; ova-nourishing cells; follicle-cells ; 
sperm-mother-cells ; and sperm-cells (various stages of development). 
g. Sexual Cells, Propagation and Development ( 11 , 18 , 31 , 
35 , 46 , 48 , 55 ). 
Seeliger (46) criticises the statements made by various authors con- 
cerning the propagation of Sponges by budding. He thinks that there is 
certainly no continuity of the germinal layers through the gemmules 
from the mother to the daughter Sponge, developed from a gemmule, 
even if— as appears more than doubtful — both ectodermal and ento- 
dermal cells combine to produce the gemmules. The propagation of 
Sponges by gemmules may, according to him, perhaps be a sort of “Poly- 
sporogonie.” 
Maas (31) criticises Wilson's statements concerning the development 
of Sponges, and upholds his formerly expressed opinion that the prin- 
ciple of blastologic development is the same in Silicea aud Calcarea : 
in both the “ ectoderm ” of the larva produces the entoderm (collar- 
cells) of the adult, and the “ entoderm ” of the larva the ectoderm 
(outer epithelium and greater part of the interstial layer) of the adult. 
Minchin (35) has studied the development of the larva of A scamlra 
( Lcucosolenia ) variabilis and other Asconidcu. The larva of A. variabilis 
is an Amphiblastula, with slender flagellated cells in the anterior, and 
broader, nou-flagellated, granular cells in the posterior region. The 
central part of the larva is occupied by brown pigment. The pos- 
terior, granular cells, originally less numerous than the anterior flagellated 
ones, afterwards become relatively more numerous, because the flagel- 
lated cells are — at the border line between the two kinds of cells— 
continually being converted into nou-flagellated granular elements. 
The cells being thus converted form an intermediate zone. The 
flagellum of the flagellated cells arises from the onion-shaped nucleus. 
The central pigment mass has the shape of a tube. The lumen of this 
tube is occupied by a subspherical space filled with granules, supposed to 
be the remnant of the segmentation-cavity. Several cells are in this 
stage observed, lying below the superficial granular elements, so that the 
larva is no longer a blastula composed of a single cell-layer. The larva 
attaches itself with the anterior end, and the granular cells overgrow it 
entirely. The attached larva is composed of two cell layers : a single 
layer of flattened cells on the surface and a compact* mass of polyaedric 
cells in the interior. No trace is left of the former central cells, which 
appear to be thrown out together with the pigment during the meta- 
morphosis. The inner mass is the future gastral layer ; the outer 
epithelium the future dermal layer. The rapidity with which these two 
layers develop further is not constant : in this respect the two are 
independent of each other. The outer cell layer (epithelium) is soon 
differentiated into two layers : an outer continuous epithelial, and an 
inner subepithelial layer, which latter is represented by scattered cells 
only. In each of the epithelial cells one monaxon spicule is formed, 
which soon grows so as to project considerably from the surface. The 
subepithelial cells unite into groups, and produce the triactines. 
Monaxones appear about twenty-four hours after fixation, the triactines 
twelve hours later. The inner cells (gastral layer) become cylindrical 
and radially arranged round a cavity, originally split-like, which is 
formed in the centre, and rapidly increases in size. In one place, how- 
ever, the radial cells are missing, and here the dermal cells only compose 
