The testis itself, in a recent specimen, is so large as to occupy a very considerable part of the abdominal cavity: it is nearly transparent ; and when portions of it are examined under the microscope, its substance seems to be en tirely made up of minute tubes, connected to gether by delicate membranous processes. Its external convex surface (fig. 113. 28) is convo luted, so as to give it the appearance of being a hollow vesicle three times folded upon itself ; whilst its inferior concave surftce exhibits under the microscope a reticulate appearance, something like that of the stomach of a ru minant quadruped.
The cominon outlet of the ovary, of the bladder, and of the testicle is short, but toler ably thick. It mounts upwards, and ter minates close behind the right fin, in the im mediate vicinity of the anal orifice.
On opening the cavity of the head, by re moving its anterior wall (including the collar and the subjacent muscular layer), its contents are displayed as exhibited infig. 111. 16. Im mediately behind the contracted conical append ages, and close to their hollow bases, is seen a long milk-white organ (b), which, in old specimens, is so extremely brittle, that it is generally broken in the dissection. Behind this, and close to the collar, lies a red sac culus not easily to be displayed ; and, in the neck itself, immediately upon the collar, is situated a single loop, formed of the same white substance as b.
On carefully unfolding these parts, they are found to present the structure displayed in fig. 113. 26, the transverse body (b) and the loop (c) constituting portions of the same viscus. The transverse portion is a canal
terminating by a blind extremity (a), while the loop itself may be displayed as an ex tremely attenuated canal (d) of a reddish colour, which, after several convolutions, opens into the red sacculus (g), and ultimately ter minates in another short, but wider, tube (f the common orifice of the sacculus and of the convoluted canal is a wide, longitudinal opening, situated in the cavity between the right fin, the head, and the collar. On cutting into this canal, it is found that the milky colour it presents is but slightly owing to the nature of its contents, depending principally upon the texture of its walls, which, when ex amined under the microscope, are found to contain numerous granular bodies, which are apparently of a glandular character, united to gether by a very thin and transparent mem brane, the delicacy of which readily accounts for the fragility of the tube.
The structure of the red sacculus (g) is not yet fully understood. Its walls are in some parts very thin, and on opening it, the tube ( f) is seen to be continued through it.
Eschricht was, at first, in considerable doubt as to the nature of this remarkable apparatus : he observed, however, that in several spec], rnens, a portion of the sacculus was inverted and protruded externally in the shape of a long bow-shaped organ (fig. 114. 3, h), along the cavity of which a delicate canal could be distinctly traced, the bow-shaped organ being manifestly the penis, everted in the same way as in many Gasteropod Mollusks, and the de licate canal constituting the vas deferens.