32 
DE. G. EOLLESTON AND ME. C. EOBEETSON ON THE AQHIEEEOHS 
organ of Bojanus, and supported in water with its foot downwards in such a manner a 
to put its pericardial lacuna, and the parts in connexion with it, as nearly as possible 
into the condition in which they may be supposed to be in in the shell during life, and 
if an injection be then made into the pericardial lacuna, the following results will be 
seen to take place. The so-called “ reddish-brown organ of Keber ” (a plexus of vessels 
rich in pigmentary deposit, continuous with other vessels not so coloured in the mantle 
and elsewhere, and boimding the pericardium on either side, and opening into it by 
several patent orifices at its anterior end) will become filled with the injecting-fluid 
first; next the gill-vessels, and sometimes together with them, yet not invariably, the 
systemic veins ; and lastly the external orifice of the organ of Bojanus will, on removing 
the animal from its prone position, be seen pouring out the injection on either side of 
the animal’s foot. 
Experiment 2. — A large Anodon was injected with a red stiffening-injection from the 
central branchial vein, a vessel readily injectible, lying as it does in the gill-cavity supe- 
riorly between the two innermost laminae of the gills, in the angle where they become 
continuous with each other posteriorly to the posterior edge of the foot, with the follow- 
ing results : — The auricle and ventricle were filled to distention, the reddish-brown organ 
as well, and, besides the reddish-brown organ, the rest of the mantle, up to within a 
quarter of an inch of its free edge. No fluid, however, had penetrated into the pericar- 
dial space. The absence of penetration into the pericardium we have invariably had to 
record in our numerous injections from the branchial veins, even when the injection is 
noted as having been so entirely successful as to have passed through the aorta in such 
abundance as to inject in flne ramuscular divisions the edge of the muscular foot. 
The former of these two experiments is so easy of performance, and yet proves so 
much, that we cannot but express our surprise at nowhere finding any record of its 
ha^ing been made by any of the different experimenters who have employed injections 
as a method for investigating the economy of mollusks. We have repeated it so fre- 
quently with the same results, as to have become quite convinced that the pericardial 
lacuna communicates, on the one hand, with blood going gillward, and on the other 
with the water in which the animal lies. 
The uniformity with which our repetitions of Experiment 2 have led to the same nega- 
tive result inclines us to doubt the existence of any direct communication between the 
aquiferous pericardial lacuna and the branchial veins properly so called. We are the 
more disposed to accept this conclusion, as in no mollusk whatever which is possessed 
of branchial vessels, except the Pleurobranchus* , has the renal organ been shown to con- 
duct the external water into the cavity of vessels homologous, not with the afferent, but 
with the efferent f branchial vessels of higher organisms. 
Though Experiment 2 may seem to prove that the intravascular blood does not set in 
any very free current outwards into the pericardial space, especially when coupled with the 
observation that in multitudinous and varied injections of the different systems of blood- 
* M. Lacaze Detheees, Eoyal Society’s Proceedings, loc. cit. t Gegenbaue, Grundziige, p. 367. 
