810 
DE. J. S. BOWEEBAl^K ON THE ANATOMY 
Professor Leidey, and Professor Dawson, of College, Montreal, Canada. The 
greater portion of these organs resemble each other very closely in their natural condi- 
tion, presenting generally the appearance of a more or less spherical coriaceous body; 
but the structure of their walls, when developed by treating them carefully with hot 
nitric acid, is so varied and strikingly characteristic of their organic and specific differ- 
ences, as to render it necessary that I should enter somewhat minutely into their history. 
Their structual peculiarities naturally divide them into two great groups. 
1st, those in which the walls of the ovaria are strengthened and supported by 
birotulate or unirotulate spicula radiating in lines from the centre to the chcumference 
of the ovarium ; and 2nd, those having the walls of the ovaria supported by elongate 
forms of spicula, disposed on or near its surface at right angles to lines radiating from 
the centre to the chcumference of the ovarium ; and, fortunately, the types of these two 
forms of spicular arrangement on the cortex of the ovarium are admirably illustrated in 
the two Em’opean species of Spo7igilla, the first mode existing in Sjpo^igilla Jluviatilis, and 
the second one in S. lacustris. After having described the ovaria of these two species 
as types of their respective groups, I shall, in my future descriptions of these organs, 
confine my observations rather to their anatomical structure than to their external 
characters, excepting when the latter are of an unusual description. These bodies occur 
in great profusion in the basal portions of S. Jluviatilis ; they are spherical and of an 
average diameter of -^th of an inch, and they are furnished with a circular foramen at 
their distal extremity of about x|^rd of an inch in diameter. In their natural condition 
they exhibit very slight indications of the birotulate spicula imbedded in their coriaceous- 
looking envelope. In the dried state they become cup-shaped by the contraction of the 
upper half inward during the process of desiccation, and in this condition the foramen 
appears at the bottom of the cup. The edges of the cup being thick and round in con- 
sequence of the presence of the birotulate spicula beneath the fold of the membrane, 
the surface becomes pitted with numerous minute lacunae, which are produced by the 
adhesion of the inner surface of the envelope to the distal extremities of the birotulate 
spicula. Immersion in water for an hour restores them to their spherical form, but 
does not obliterate the lacunae produced by desiccation ; and I have several times observed 
that, under these circumstances, the expansion of the ova withm has forced one or more 
of them through the foramen. 
If we take several of the ovaria, either in the living condition or in the expanded 
state I have described above, and place them in a test-tube with a little nitric acid, and 
raise the temperature of the whole until the ovaria become of a bright yellow colour 
and semitransparent, and then arrest the operation of the acid by immediately pouring 
in a quantity of cold water, we shall have preserved their form and have retained the 
spicula in their natural positions, and have rendered the whole so transparent, as to 
exhibit their form and arrangement in the walls of the ovarium, either in water or 
mounted in Canada balsam, in a very beautiful and satisfactory manner. They are 
packed very closely together, their shafts being in lines radiating from the centre of the 
