426 Royal Society : — 



the presence of the posterior cornu and hippocampus minor through- 

 out the different members of the group ; and hence a most important 

 character is supplied for determining the affinities of these interesting 

 animals. It indicates as decisively their position among the Qua- 

 drumana, as it separates them completely from the Insectivora, in 

 which order some naturalists have placed them. 



Many links are still wanting in the chain of evidence required to 

 determine the true history and classificatory value of the posterior 

 horn of the lateral ventricle, and the peculiar disposition of cerebral 

 substance constituting the hippocampus minor ; but the conditions 

 in which tbey have been found at so many distinct points of the 

 series, appear to lead almost irresistibly to the following conclusions : — 



1. That these parts, so far from being (as has been stated by some 

 anatomists) peculiar to the human brain, are common to man and 

 the whole of the Quadrumana, including even the lowest forms. 



2. That they attain their maximum of development in species 

 which do not belong to either extremity of the series. 



3. That in the lower forms their diminution takes place chiefly 

 in the antero-posterior direction, corresponding with the reduced 

 length of the posterior cerebral lobes, the greater part of which is 

 occupied by them. 



4. Tbat in the higher forms they are narrower in proportion to 

 their length, and bear a smaller ratio to the surrounding mass of 

 cerebral substance. 



5. That the extreme of the last condition is met with in man, 

 where these parts are also characterized by their variability in size 

 and form, want of symmetry on the two sides, and frequeut rudi- 

 mentary condition, or even entire absence. 



Communication received August 20, 1862. 



" On the Aquiferous and Oviducal System in the Lamellibranchiate 

 Mollusks," by George Rolleston, JV1.D., F.L.S., Linacre Professor 

 of Anatomy ; and C. Robertson, Esq., Demonstrator of Anatomv, 

 Oxford. 



After recapitulating the views which have been held by various 

 authors as to the means by which certain Lamellibranchiata are 

 enabled to distend their muscular foot, the authors of this paper 

 proceed to make a retractation of the opinions they put forward as 

 to the oviducal system in these mollusks in a paper read before the 

 Royal Society, February 3, 1859. But, though they have some 

 reason to agree with M. La Caze Duthiers's views, as expressed in a 

 paper read before the Royal Society, December 15, 1859, so far as 

 the oviducal outlet is concerned, they are not prepared to coincide 

 with that writer in denying altogether the existence in these animals 

 of an aquiferous system distinct from their blood-vessels. Upon this 

 point their views remain much the same as those they enunciated in 

 their paper already referred to, and they may be briefly summed up 

 thus. 



They hold that, side by side with, and yet distinct from, the blood- 

 vascular system in the Lamellibranchiata, there exists another sy- 



