134 
THE GEOLOGIST. 
triumphantlj produced by the anti-transnnitationists ; if, on 
the contrary, it has changed in ever so slight a degree from an 
extinct form it is called a new species. 
4. Suppose a large area covered with sea, and Lingula, &c., spread 
over it. Now suppose a part of this area to be gTadually 
elevated, the Lingulse and other animals living on it would 
undergo variation to meet the change of conditions ; but those 
on the stationary area would remain constant. Next suppose 
the elevated part to sink again : the new forms on it must 
either die out or change, and the Ling-ulae would again spread 
over the whole area ; and being better adapted to those con- 
ditions, from long residence in them, would kill off, perhaps, 
some of the new forms. Again, another part of the area 
might be raised : and so on. -The chances are that some of 
the Lingulse would always be on a stationary portion, and thus 
hand down their offspring with little variation, for any length 
of time. It is a fact which strongly corroborates this, that 
nearly all the genera which have a long range in time are 
inhabitants of the deep sea, and therefore have also a large 
range in space. 
5. It is not supposed that the armadillo is descended from the 
glyptodon ; on the contrary the latter seems to have become 
extinct, and to have left no progeny, while some other form 
may have been the progenitor of the former. 
6. " On the contrary domestic breeds show all degTees of variation, 
as the pigeon, dog, &c., on one side, and the cat and goose on 
the other. Perhaps there is not much difierence of variability 
in animals, constancy can generally be accounted for ; pigeons 
can be mated for life, and are kept in large quantities, and 
therefore vary much ; cats ramble at night and cannot be 
watched, and are kept in small quantities ; donkeys and pea- 
cocks are also kept in smalt-qtianTities, and the breeding of 
donkeys is not much cared for ; geese are only valued for 
two purposes, food and feathers, and no pleasure seems to have 
been felt for different breeds." 
Let us now see what reasons there are for supposing ttiat variation 
is at preseyit unlimited ; or, in other words, that all animals have de- 
scended from a common prototype. By admitting it to be true we 
can easily understand — 
1. Why species have come into the world slowly and successively 
2. AYhy " the families of each division (of moluscs) which are least 
unHke (OrthoceraticlcB and Belemnitidce) were respectively the 
first developed.* 
3. Why species have not necessarily changed together, or at the 
same rate, or in the same degree ; yet in the long run all have 
undergone modification to some extent. 
* Woodward's " Recent and Fossil Shells/' p. 417. 
