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the measure, possibly, of several lost strata ; and we do not know how many 
such there may have been. I was rather puzzled to understand one par- 
ticular reference to the coming in of new forms ; Dr.'Nicholson said we 
seemed to be certain that sometimes we arrived at the first beginning of a 
new form : this idea rests solely upon negative evidence, unless he refers to 
some of the graduated forms ; as, for instance, to one of those species of 
Orthis or Spirifera to which the paper refers : but when we suddenly come 
to a new species or genus, we have no ground whatever for assuming that it 
is the first, and the only explanation (unless we fancy it was created then and 
there, which we should hardly do) is that it must have migrated. I think 
the negative evidence is all in favour of migration, wherever we come across 
a permanent type for the first time ; but so long as it is one of a graduated 
scries, I think we might be justified in saying that it is probably its first 
commencement. With reference to the horse group of which Professor 
Nicholson spoke, in which there are not fine intermediate links, it must be 
borne in mind that evolutionists generally do not necessarily require such 
fine links, though Mr. Darwin’s theory of natural selection does. Mr. Darwin 
requires extremely small variations, but the question really turns upon this : — 
how much difference is really required between one form and another ? 
Mr. Darwin requires a succession of slight differences, and palaeontology does 
not always give them : but may it not be true that some of the higher types 
of life are formed by “ sports” — by slight leaps, as it were, instead of by 
minute gradations ? I should like to ask Dr. Nicholson, as being a better 
palaeontologist than I am myself, whether it may not turn out to be a law 
applying to the higher types, that the distances between them are rather 
greater than is the case in the lower ; the horizontal modifications, for in- 
stance, being more numerous and more varied, in comparison with the vertical 
modifications. Take the Foraminifera among animals, or the agarics among 
vegetables, and there you have simple organisms, but there is an enormous 
amount of variety amongst them — perhaps hundreds of thousands : they 
are low types, on a common level, as it were, varying to a very great extent ; 
and I would ask, would not Dr. Nicholson’s experience support the idea that 
the lower the type, the greater the amount of horizontal modification ; but 
that when you get to the higher forms the modifications come by jumps and 
leaps ? I should like to know whether that idea has been found to be the 
case? It certainly would clear up the difficulty that Dr. Nicholson has 
pointed out ; — that in the higher groups especially there are these breaks, 
and that you do not get a graduated series such as you find among the lower 
types. 
Mr. J. E. Howard, F.R.S.— I think we are all indebted to Dr. Nicholson 
for this very able exposition of views, in which, for my own part, I entirely 
agree. So far as my knowledge extends, there is certainly a law of varia- 
bility which prevails among some species very much more than among others, 
and which I have sometimes compared to the swing of a pendulum. If wo 
