545 
of Edinburgh , Session 1868-69. 
i'utation of Berkeleyism. For the mind not only possesses a com- 
mand of physical power, but it is conscious that it possesses it, and 
that it exerts it, and that its exertions are resisted by external 
objects ; and thus, through a direct consciousness of mental power, 
we have an indirect, hut indefeasible proof and perception of the 
resistance of external objects, and of the external world. 
3. On the Affinities and Classification of the Nemerteans. 
By W. C. Mlntosh, M.D., &c. 
The immediate allies of the Nemerteans are evidently the Plana- 
rians, and Ehrenberg’s class Turbellaria , as now amended, is there- 
fore a very natural one. There is, however, a considerable divergence 
between the two groups ; and since it is only through the Planarians 
that the Nemerteans can in any way be linked on to the Trematoda, 
it is found that there is little structural resemblance between the 
two last-mentioned types. The various parts of the organism in 
the Trematodes and Planarians (through which the connection of 
the Nemerteans with the former may be supposed to occur) were 
contrasted, and their homologies explained. The structural re- 
lations of the Planarians and Nemerteans were then considered ; 
and, thirdly, the connections of the latter with the higher Annelids 
were alluded to. 
In regard to classification, the arrangements of Linnseus, Ehren- 
berg, (Ersted, Be Quatrefages, Max Schultze, Schmarda, Keferstein, 
and others were examined, and the reasons why they could not now 
be adopted, at least without essential modifications, explained. 
The following classification is considered less liable to alterations 
in principle, since it is founded on an anatomical basis. 
Order Nemertinea. — Worms, with more or less elongated, soft, 
ciliated bodies ; nervous system composed of two conspicuous 
ganglia connected by a double commissure, and two main lateral 
cords ; digestive system, in the form of a ciliated canal, with two 
apertures; circulatory system, consisting of a series of closed con- 
tractile vessels. The proboscis forms the typical organ of the 
order, and is surrounded by a special muscular sheath, within which 
it glides in a corpusculated fluid ; in front it passes between the 
commissures of the ganglia, while the digestive tract is placed 
