AND OYIDTJCAL SYSTEM IN THE LAMELLIBEANCHIATE MOLLUSKS. 
37 
There is no difficulty in causing an injection to enter the body of any large individual 
of the family Unionidae from its oviducal orifice ; it is especially easy, however, to effect 
this in the Xlnio margaritifera, as the orifice is not in them, as in most species of the 
family, covered by the inner lamina of the inner gill, but, together with the orifice of 
the organ of Bojanus, lies exposed and uncovered in the gill-cavity, and, besides this, 
is prolonged out in such a manner as to render the introduction of the syringe-pipe a 
very easy matter. 
Experiment 6. — An injection thrown in by this orifice will spread itself over the 
whole of the \iscera contained within the foot, not confining itself by any means to the 
ovary, but passing on beyond the area occupied by it or the male generative gland, 
into the exclusively muscular part of the foot, and distributing itself with especial rich- 
ness along its free edge. That an injection thrown in by this orifice should thus spread 
itself would go some way towards showing that in the Lamellibranchiate, as in the 
Brachiopod mollusk, the ducts through which the generative products are extruded 
lead elsewhere as well as to the generative gland, were it possible to be sure that no 
transference of the injected fluid had taken place from tubes confessedly in connexion 
with the generative gland to another system of vessels — that, namely, which carries the 
blood. That such a transference does not rarely take place in one part of the blood- 
vascular system, we have afready mentioned * ; and hence arose the necessity for double 
injections, in which the blood- vascular system was (as has been and will again be 
described) injected and fully distended throughout the entirety of its own ramifications, 
before any fluid was thrown into the oviducal orifices, and by still mapping out a tree 
for itself, showed the independence of the system it led to. Single injections, however 
inferior to double ones, still furnish us with strong arguments for the view we are sup- 
porting. A freshwater mussel may have its whole visceral mass perfectly injected, 
either from the blood-vessels or from the oviducal system ; but when thus injected, a 
practised eye has no difficulty in seeing into which of the two systems the injection has 
been thrown. The blood- vascular injection is seen to be contained in coarser tubes, 
and to form a less close network than the aquiferous, which, though confined within fine 
capillaries, gives, till closely inspected, an appearance almost of uniform diffusion, on 
account of the closeness of the network it forms. 
Secondly, we will give the details of two double injections. 
Experiment 7. — A double injection from the venous system and the oviducal in the 
same Anodon. A stifiening size injection of red colour was used for the oviducal or 
aquiferous system, and the prussian-blue injection, a more easily running fluid, for the 
venous system, with the following results. The red injection occupies the area corre- 
sponding to the generative gland, with coarse as well as mth fine twigs, has imparted a 
faintish blush to the regions occupied by the liver and stomach, but has filled the interior 
of the exclusively muscular portion of the foot with so close and fine a network as to 
give it at a distance a uniform red appearance. The blue injection occupies much of the 
* Note, p. 36. 
