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



LI. On the Aquiferous and Oviducal System in the Lamelli- 

 branchiate Mollusks. By George Rolleston, Esq., M.D., 

 F.L.S., Linacre Professor of Anatomy; and C. Robertson, 

 Esq., Demonstrator of Anatomy, Oxford*. 



Very different explanations have been offered of the means by 

 which certain of the Lamellibranchiata are enabled to distend 

 their muscular foot until the fluid with which it is swollen up 

 causes it to appear all but transparent. These explanations, dif- 

 ferent as they are both in principle and in detail, admit yet of 

 being reduced under one or other of three heads. Either they 

 postulate the existence of a system of tubes homologous with 

 the tracheae of insects, and, like them, distinct from the animal's 

 blood-vessels, as necessary for the explanation of the great 

 changes of volume observed to take place in the mollusk's body; 

 or they suppose these alterations of size to be effected by the 

 agency of the blood-vascular system alone ; or, thirdly, they hold 

 the effect in question to be due to the joint working of these two 

 systems of tubes. 



Agassizf refers the great distention observable in the foot of 

 the Natica heros, of the Pyrula carica and canaliculata , and the 

 Acephalous Mactra solidissima, to water inhaled by orifices more 

 or less numerous, of less or greater calibre, in the muscular foot : 

 these orifices, and the tubes in connexion with them, he speaks 

 of as a water- vascular system, but he holds that they come into 

 more or less direct and constant communication with the true 

 blood-vascular system. 



Theodor von Hessling J, who obtained the same result of in- 

 jecting fully the blood-vascular system, by throwing in fluid from 

 the glandular depression in the foot of the Unio margaritifera, as 

 Agassiz did by a similar procedure with the similar depression 

 in the foot of the Gasteropodous Pyrula, speaks of the system 

 (which on these grounds he holds to be continuous) as but one 

 system and that a blood-vascular system, with certain orifices 

 patent and communicating with the external medium in which 

 the animal lives. Von Hessling holds also that the distention 

 of the foot may be in part due to water inhaled through the 

 organ of Bojanus, and mingled thus with the blood, as we shall 

 presently describe. 



M. Langer§ holds that the organ of Bojanus is the route by 

 which the water, upon which the change of volume in the animal's 

 body depends, passes into it, and that this water passes into the 

 blood-vessels, and not into any specialized water-vascular system. 



* From the Philosophical Transactions, Part I. for 1862, p. 29. 

 t Zeitschrift fvir wiss. Zoologie, Pt. 7. p. 176", 1855. 

 X Perlmuseheln und ihre Perlen. Leipzic, 1859 : p. 241. 

 § Denkschriften d. Kaiserlich. Akad. Wiss. xii. p. 55, 1856. 



