812 
BE. J. S. BOWEEBANK ON THE ANATOMY 
MS., from the Eiver Amazon, represented by figs. 23, 24, 25 & 26, Plate XXVI. Phil. 
Trans. 1858. 
A gradual transition from the birotulate form to that of the unirotulate one takes 
place in the ovaries of S. paukila (fig. 31) and S. reticulata (fig. 33), until we obtain the 
perfect and beautiful unirotulate form in the ovaries of 8. recurvata., represented by 
figs. 34 & 35 in the Plate quoted above. In all these species there is a general accord- 
ance in the mode of their structure. 
The gradual transition from the birotulate to the unirotulate form of spiculum in the 
ovaries of Spongilla reticulata is not the only characteristic difference that exists between 
it and its congener. The form and structure of the ovarium also exhibit marked pecu- 
liarities of character, and it is also furnished with a beautiful reticulated spicular enve- 
lope or case. In its natural condition the ovary fills the reticulated case, and the 
coriaceous external surface is pressed into the areas of the network. 
It is usually oviform, but it varies to some extent in its shape. When treated care- 
fully with hot nitric acid, the outer coriaceous substance of the ovarium is dissolved, 
leaving the inner membrane and the boletiform spicula in situ ; their larger termina- 
tions being applied to the distal surface of the membrane, while their smaller clavate 
or stellate ends are projected outward, reaching, in the natural condition, to very near 
the external surface of the ovarium. The foramen is situated at the small or distal 
end of the ovary, and differs from that of any other form of the organ with which I 
am acquainted, inasmuch as it exhibits a tubular elongation outward of the lining 
membrane equal in length to about its own diameter, causing the ovarium, when 
prepared with nitric acid, to appear like an oil-flask with a very short neck. Fig. 13, 
Plate XXXIII. represents one of the ovaria prepared with acid, and fig. 12 one of the 
cases in which they are contained. 
In Spongilla Brownii, Boweebajstk, MS., there is a still further deviation in the 
structure of the spicula of the ovary. The shaft entirely disappears, and the spiculum 
is reduced to the umbonato-scutulate form. They are situated on the outer surface of 
the inner membrane of the ovarium, with the umbones of the scutellae outwards. This 
mode of disposition obviously renders them inefficient for external defence, and the 
ovaries have therefore been further defended by being enclosed within an elaborately 
constructed case of reticulated acerate spicula. The gemmule is closely embraced by 
this envelope, and small elongate masses of its outer surface are projected through some 
of its interstices, causing it to be more or less tuberculous ; and, from the smallness of 
the interstices, the tubercles of the envelope of the ovary are much greater in length 
than in thickness. The spicula of the case are disposed in a close and irregular net- 
work, seldom exceeding two spicula in thickness. By a careful treatment with hot 
nitric acid, the thick coriaceous outer portion of the ovarium may be removed, and its 
thin lining membrane, with its stratum of umbonato-scutulate spicula, becomes an exceed- 
ingly beautiful object. The same mode of operation displays the structm’e of the reti- 
culated case of the ovary very much more distinctly than when viewed in its natiu’al 
