3U4 
liemarking upon the number of recent species of Mollusca, ho 
observed, “that we have a catalogue of sixteen thousand shells 
which Avants revision from beginning to end ; and among the 
benefits likely to arise from the revision, not the least Avill be the 
reduction of perhaps one-fourtli of these reputed species to the rank 
of mere varieties.” “To this pervading fault may be attributed a 
good deal of the scepticism res|)ecting the ‘ reality of species,’ of 
Avhich wo have lately heard so much.” It may bo interesting to 
quote Avhat he says on this subject. 
“Linnaeus, with his usual felicity of expression, has given us liis opinion 
respecting genera and species : 
“ ‘ Classis et orJo est sapientiae, species naturae opus,’ 
whicli may be freely translated, ‘ Species are real ; genera, ideal.’ The mar- 
shalling of species in classes and orders is matter of discretion ; but species 
themselves are the work of God. It is an axiom in natural history, as in 
philosophy, that like produces like; and, as this is the result of all human 
experience, we have come to regard relationship by descent as the essential 
quality constituting identity of species. Absolute agreement in size and 
appearance is not expected, since we must all have observed how greatly the 
individuals of one brood may differ ; but it is only by long and frequent 
observation that we can tell in what respect and to what extent these 
variations may occur. Dredge up a thousand shells of Astarte com2rressa 
in Berwick Bay, and you may select from among them half-a-dozen more 
deeply furrowed than the rest, many which are less distinctly marked than 
the average, and a few quite smooth and polished. 
“ The town naturalist to whom you show the selected series might reasonably 
conclude that there were at least three species, unless he had previously seen 
instances of the kind. Gregarious shells, like the common whelk and peri- 
winkle, which occur in very great abundance, are more prone to vary than 
others ; but these variations occurring at the same place are individual, and 
not hereditary ; whereas variations peculiar to different localities occur 
amongst all widely-distributed species, and constitute permanent varieties or 
races. Hence the idea of a ‘species’ is not so simple or readily expressed 
as at first might appear. It generally includes — as in the case of our own 
species— many permanent races (each composed of individuals differing more 
or less from one another), distributed over a definite geographical space, and 
related— more or less remotely— by descent. 
“A genus in like manner, is a group of species, related to each otlicr 
topographically , just as races are related to species. Upon this point the 
best naturalists are agreed. But the same inference with respect to 
relationship by descent does not necessarily follow, and is rendered at least 
improbable by the evidence of fixity of species wliich pal.-eontology aflbrds. 
