31 
from the common centres. Colonies of species, started at particular times in 
different formations, have spread to immense distances, and their track can 
be traced by the persistency of type which characterizes almost all the 
species, until suddenly they come to an end, and a new form as suddenly 
occupies their place. Every specimen contained in museums all over the 
world has been examined by the most competent naturalists, to find a single 
clear case of development, or a repetition of the same species in this immense 
family, but at present without success. The numbers of the lowest organisms 
have never decreased ; therefore there can have been no general system of 
progressive development from some low organic type.* As to the law of 
changes, the late Mr. Babbage made this suggestion : That you might 
make a machine to go on with a clock, with a particular series of differ- 
ences, for thousands of years ; and then, by an automatic change pre- 
arranged in the formation you would find the series changed, and go on 
afresh, and so on for ever, the machinery carrying its law of change with 
it. That is very much the case with the family of the Brachiopoda : new 
species are constantly coming in, and old ones dying out. No one has sug- 
gested what change of condition has to do with form or sculpture of the shell 
of mollusca ; every change of form must have an object — origin, near or remote. 
We are however met by this difficulty : that there is no discernible law for a 
genus or species first coming in : it was on this ground that the great naturalist, 
Edward Forbes, believed in specific centres. If the Terebratula caput scrpentis, 
now living in the North Sea, could be fossilized, no living naturalist could 
say that it ought to belong to the present period more than to the Oolite, 
or to the Oolitic period more than to the Silurian. We have nothing to 
assist us to define the cause of change, or to help the Darwinian view of 
struggles for existence, or changes of material conditions, influencing the 
shape or size of any organ, in the case of any one species of the Brachiopoda. 
Edward Forbes had studied morphology, and yet he considered every 
individual fossil as having sprung from one pair of the particular 
primordial species. If you take man, you will find that in different 
countries he has a different brain, size, aspect, and skin, and is under 
very different modifications ; but there is no evidence of any living men 
* See Barrand’s Colonies, and Davidson’s Brachiopoda, page 264, 
1857-62 ; also page 47, Davidson’s Journal de la SocictJ Malacologie, 1876 ; 
also Murchison, King, and others on the persistency of this species with 
distribution of the species of the Brachiopoda. I quote one passage — 
“ Since the Cambrian period, both great divisions continue to be represented 
without showing any tendency to pass one into the other.” — (A. T.) Prin- 
cipal Dawson, F.R.S., in his 1874 Annual Address as President of fixity of 
species, the Natural History Society of Montreal, strongly insists on the 
giving remarkable instances among the Fauna on the coast of America 
(see note, vol. ix. p. 236). — Ed. 
