34 
DE. a. EOLLESTON AND ME. C. EOBEETSON ON THE AQriEEEOTJS 
mussel to another set of vessels, the main stem of -which has the additional function of 
outlet to the generative gland. As, however, Von Hessling* holds that the system of 
pores in the foot plays no inconsiderable part in the work of supplying the distending 
foot -with water, acting in aid of, and in alliance with, the system of the organ of 
Bo JANUS, and, with Agassiz and Von Rengaeten, as already cited, holds this office to be 
exclusively discharged by this system of pores and inlets, we -will begin by stating our 
reasons for demurring to these -views, in which we ourselves at one time participated. 
It will be necessary to give the details of two sets of experiments, to show how we came 
to give up an opinion which can plead such high authorities as those we have cited for 
its defence. 
Experiment 4. — A large Anodon, ha-vdng died -with its foot in a semidistended state, 
was injected from the venous sinus which receives the blood from the systemic veins 
and distributes it to the renal-portal system, with the prussian-blue injection already 
spoken of. The injection spread over the liver and over the whole of the generative 
gland, and the exclusively muscular part of the foot, spreading itself in especial rich- 
ness along the fi:ee edge. No pressure which we subjected the foot to, when thus fully 
injected, caused any of the blue injection, easily and readily though it runs, to issue 
forth. Subsequently to this, a stitfening injection of red colour was thro-wn into the 
foot-mass from the o-viducal outlets. This second injection spread itself very richly over 
the ovaiy, over the liver, and into the muscular foot, along the free edge of which it 
issued in small jets ivithout any ’pressure being applied. ^ 
We -will disregard, for the moment, the bearing which this experiment has upon the 
distinctness from the blood-vascular system of the system of tubes in the muscular foot, 
to which the stem opening under the name of o-viduct into the mantle-cavity leads, and 
we -will relate the details of another set of experiments, which led us to consider the 
phenomenon of the jets issuing from the foot-edge as due, in spite of the frequency -with 
which we have seen it recur, to -violence done, possibly unavoidably, to the delicate limit- 
ary tissues of these aquiferous tubes. 
Experiment 5. — A TJnio margaritifera, which had died with its foot quite relaxed, 
had the blue injecting-fluid introduced into its aorta, its venous system, and through 
the o\iducal orifices, until the foot, from a state of perfect softness, became tense and 
swollen up. On pressure, none of this triply4njected blue fhuid could be made to issu 0 
foHh from the foot-edge ; but small hernia-like projections of transparent membrane rose 
out like bubbles all along the foot-edge. They contained at first a transparent fluid, but 
after a little pressure they became fiUed with the blue injection. The thinness and 
transparency of these little sacs -will account for the rarity of their appearance, and the 
comparative frequency with which jets of injected fluid have made themselves noticed 
in the region corresponding to the ceecal endings of tubes which these sacs must be held 
to represent. The depressions and pores which do exist in the foot of the Lamelli- 
branchiate moUusk we believe to be glandular in character, and destitute of any direct 
* Perlmuacheln und ihre Perlen, p. 238 et seq. 
