292 
THE MIDDLE LIAS OF NORTHAMPTONSHIRE. 
mass in the eggs of certain Gasteropods which may or may 
not form two individuals, and a probably similar fission 
imperfectly carried out among the Vertebrates, are regarded 
as abnormalities. “ The vertebrate animal, under its 
simplest as under its most complex form, is like the 
molluscous animal in this, that you cannot cut it into 
transverse slices, each of which contains a digestive organ, 
a respiratory organ, a reproductive organ, &c. The organs of 
the least-developed fish as well as those of the most developed 
mammal form but a single physiological whole ; and they 
show not the remotest trace of having ever been divisible 
“ into two or more physiological wholes.” Embryology and 
comparative morphology of the Vertebrata respectively 
furnish evidence to show that “ that segmentation which the 
vertebrate animal usually exhibits throughout part of its 
organisation is the same in origin and meaning as the 
segmentation of a Chiton’s shell; and no more implies in 
the vertebrate animal a composite structure, than do the 
successive pairs of branchiae of the Doto, or the transverse 
rows of branchiae in the Eoiis , imply composite structure in 
the molluscous animal.” Mr. Herbert Spencer’s inference 
is, therefore, “ that the vertebrate animal is an aggregate 
of the second order, in which a relatively superficial seg¬ 
mentation has been produced by mechanical intercourse with 
the environment.” He finally says:—“We shall hereafter 
see that this conception leads us to a consistent interpretation 
of the facts, shows us why there has arisen such unity in 
variety as exists in every vertebral column, and why this 
unity in variety is displayed under countless modifications in 
different skeletons.” 
THE MIDDLE LIAS OF NORTHAMPTONSHIRE. 
BY BEEBY THOMPSON, F.G.S., F.C.S. 
PART III. 
The Middle Lias Economically Considered. 
(Continued from paye 277.) 
Building Stone.— Northamptonshire is usually regarded 
as a county possessing very little good building stone, for 
nearly all the new buildings in both towns and villages are 
built of brick. An excellent freestone is, however, obtained 
