ANATOMY, EMBRYOLOGY, PHYSIOLOGY, BIOLOGY. Spong. 9 
cells; (2) stellate cells ; (3) glandular cells, of two kinds, one secreting 
spicules, and the other occurring in a single layer, just beneath the epi- 
thelium of the Sponge, secreting slime or a cuticle ; (4) endothelial cells 
lining the embryo-containing cavities; (5) muscular cells; (6) cells, 
probably nervous, occurring round the margins of the pores ; and (7) 
reproductive cells. The ova hang from the epithelial lining of the 
inhalent canals by means of short peduncles, and project freely into the 
lumen of the canal, awaiting fertilization. After fertilization, the ovum 
probably migrates back into the ground substance, and develops near the 
wall of a flagellated chamber. The young Sponge differs but little from 
an ordinary Grantia. A case of budding was observed, in which the bud 
had the typical Sycon form . 
According to Dendy (2) the inhalant pores of Ilalichondria panicea 
lead into a system of irregular lacunne, which penetrate inwards and be- 
come smaller and smaller. The ectosome is thin. The exhalant lacunEe 
interdigitate with the inhalant ones, and arc separated from them only 
by their strands of tissue, in which lie the chambers and spicules. The 
exhalant lacunrc usually unite into oscular tubes. The chambers are 
subspherical, with a very wide exhalant opening. The collared cells stand 
a little distance apart from one another. The collars are connected by a 
very distinct Sollas’s membrane. Since the ' collared cells nearest the 
opening are shorter than those faraway from it, the membrane approaches 
closer and closer to the ground substance, and finally seems to run into it 
at the opening. The collared cells have distinct flagella, coexisting with 
the membrane, aud are connected with one another by protoplasmic 
strands at the base. There appears to be no opening in the Sollas’s 
membrane at the prosopyles, and it probably serves for filtering food- 
particles from the water. In Sponges with large prosopyles, e.g ., Sycons, 
it probably does not stretch across the prosopyle, but ceases at the margin. 
The ova in Ilalichondria panicea are suspended by a peduncle from the 
walls of lacunes, probably inhalant. The ovum is coarsely granular 
The nucleus has a very thick membrane, and is finely granular, with a 
single spherical nucleolus, excentrically placed. 
Dendy (4) describes the Organization of the Olynthus type, and the 
Histology and Canal System of the Calcarea homocccfa. The ectoderm 
consists of a flattened, non-ciliated epithelium. The collared cells of the 
endoderm vary somewhat in different Sponges. In Leucosolenia pvoxima 
the collars may come into contact at their margins, without forming a 
distinct Sollas’s membrane. In L. Iripodifcra the collars are united by a 
Sollas’s membrane, which is peculiarly modified ; its outer surface is 
thickly studded with delicate rod-like processes of uniform length, and 
projecting from it into the gastral cavity. The mesoderm consists of 
ground substance, which is feebly developed and free from granules, and 
contains— (1) Stellate connective tissue-cells, very abundant. In Leucoso- 
lenia proxima these cells have grown out between the collared endoderm 
cells into the gastral cavity, forming a delicate network, pi. viii, fig. 2. 
(2) Amoeboid wandering cells. (3) Perhaps subdermal gland cells. (4) 
