450 Dr. G. Rolleston and Mr. C. Robertson on the Aquiferous 



The former of these two experiments is so easy of perform- 

 ance, and yet proves so much, that we cannot but express our 

 surprise at nowhere finding any record of its having been made 

 by any of the difi'erent experimenters who have employed in- 

 jections as a method for investigating the economy of mollusks. 

 We have repeated it so frequently with the same results, as to 

 have become quite convinced that the pericardial lacuna com- 

 municates, 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 negative 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 Pleurohranchus *, has the renal organ been shown to con- 

 duct the external water into the cavity of vessels homologous, 

 tiot with the afi'erent, but with the efferent f branchial vessels 

 of higher organisms. 



Though Experiment 3 may seem to prove that the intravas- 

 cular blood does not set in any very free current outwards into 

 the pericardial space, especially when coupled with the observa- 

 tion that in multitudinous and varied injections of the different 

 systems of blood-vessels we have never succeeded % in filling the 

 pericardium from the blood-vessels, easy though it be, as in 

 Experiment 1, to make the injected fluid take the reverse direc- 

 tion, more direct evidence is yet needed in support of our view 

 of the organ of Bojanus as the channel for an inwardly-setting 

 current of water. The following considerations seem to us to 

 show conclusively that, though Experiment 1 shows that it is 

 possible for intrapericardial fluid to find its way outwards through 

 the renal organ, such is not the direction usually taken by the 

 fluid contained in the complex aquiferous system thus consti- 

 tuted. 



1st. If we examine with the microscope the fluid contained in 

 the pericardial space^ we shall find it to contain, besides the 

 morphological elements of blood, certain foreign bodies, such as 

 the Aspidogaster conchicola and infusoria. Now these creatures 

 must be supposed to have found their way inwards through the 

 organ of Bojanus. 



* M. Lacaze-Duthiers, Ann. Nat. Hist., he. cit. 



t Gegenbaur, Grundziige, p. 367. 



X M. Langer's language (Denkschriften d. Akad. Wiss. he. cit. p. 43), 

 in describing his success in such injections, is so quahfied, " und sah, dock 

 nicht immer," as to allow one, without discourtesy, to give less weight to 

 his views on this than on most other points. 



