456 Dr. G. Rollcston and Mr. C. Robertson on the Aquiferous 



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 ramifica- 

 tions, 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 supporting. 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 capil- 

 laries, gives, till closely inspected, an appearance almost of 

 uniform difiusion, 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 stiffening size injec- 

 tion 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 corresponding to the generative gland, with 

 coarse as well as with 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 foot-mass in common with and interposed between the red, 

 its larger trunks holding the same position relatively to the 

 larger red trunks as the larger systemic veins do to the larger 

 generative ducts, but it has spread itself into the gills, which the 

 red fluid has not. 



Experiment 8. — A similar one to the preceding, but that the 

 blood-vascular system was distended with the fluid used in 

 Experiment 7 for the aquiferous, and vice versa. The red fluid 

 was thrown in by the aorta, it filled a large artery running 

 parallel with the cap of the foot, it filled both labial tentacles, 

 and it set, as it stiffened, in bossy masses along the edge of the 

 foot, lastly it returned to the venous sinus and filled it and the 

 organ of Bojanus, — occupying thus the entire systemic and 

 renal-portal vessels. The blue cold injection was thrown in by 

 the orifices through which the generative products are extruded ; 

 and we shall see that it, when thus thrown in, disclosed the 

 existence of a system of vessels distinct from those already so 



