AND PHYSIOLOGY OP THE SPONGIAD^. 
811 
ovarium to the circumference ; their distal rotulse supporting the outer surface of its wall, 
while the proximal rotulse sustain the inner one. Fig. 8, Plate XXXIII. represents 
a portion of one of these prepared ovaria, and fig. 8 a one of the detached spicula. Two 
views of this form of spiculum are also represented in Plate XXVI. figs. 27 & 28, Phil. 
Trans. 1858, and a perfect ovarium prepared by acid by fig. 9, Plate XXXIII. 
Caetee, in his paper “ On the Freshwater Sponges in the Island of Bombay,” in 
describing the birotulate spicula of the ovaria of Spongilla Meyeni and plumosa^ species 
with ovaries of very similar structure to those of 8. fluviatilis, states that the spaces 
between the rotulse are “filled up with a white siliceous amorphous matter, which 
keeps them in position.” I am indebted to the kindness and liberality of the author 
for specimens of these species, and I have frequently subjected their ovaries to the 
action of hot nitric acid, but I have never succeeded in finding any intervening siliceous 
matter, nor have I ever found any such siliceous cementing material in any other simi- 
larly constructed ovary of a 8pongilla. 
In the second group of ovaries of the Spongilladse, represented by those of 8 . lacus- 
tris, in which the walls of the ovaiium are supported by elongate forms of spicula disposed 
at right angles to lines radiating from its centre, the ovaria, in their natural condition, 
exhibit but very slight traces of the spicula imbedded in their walls. When dried, they 
cup inward like those of 8. lacusfris ; but the margin of the cup is thin and sharp com- 
pared with that formed in a similar manner by those of 8. Jluviatilis, and they expand 
also in like manner when immersed in water. When treated with hot nitric acid they 
display an abundance of short, stout, entirely spined, subarcuate acerate spicula, one of 
which is represented in Plate XXVI. fig. 13, Phil. Trans. 1858. These spicula are in 
many instances exceedingly numerous ; they are disposed without order, and overlie each 
other at various angles, forming, in their imbedment in the envelope, a strong and very 
efficient irregular network of spicula. A portion of one of these prepared ovaria is repre- 
sented in Plate XXXIII. fig. 10. 
In the ovaries of the different species of 8j)ongilla, to be arranged hereafter in accord- 
ance with their structural peculiarities, there is a considerable amount of general resem- 
blance, but accompanied with such permanent variations in the structure of the spicula, 
and in other portions of the development of these organs, as to render a somewhat 
detailed description of them necessary. Thus, in the development of the birotulate 
spicula, the ovaries of 8pongilla jilumosa, Caetee, exceed any other known species. 
The thick walls of these organs are filled with them in the state represented by fig. 21, 
Plate XXVI. Phil. Trans. 1858, and the intervals between their shafts appear to be 
filled with indurated sarcode or keratode. In 8pongilla Meyeni, Caetee, the walls of 
the ovaria are strikingly similar in their structure to those of 8. Jlumatilis, and the form 
of the spicula the same, with the exception of the shafts being very much more spinous, 
and the size of the spiculum twice that of 8. flmiatilis. Fig. 29, Plate XXVI. Phil. 
Trans. 1858, represents a spiculum from an ovary of 8. Meyeni. The smallest and 
most simple development of birotulate spicula exists in 8])ongilla gregaria, Botveebane, 
MDCCCLXII. 5 s 
